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documentation/user-manual/Makefile

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+.PHONY : all clean archclean single
+
+all: single
+
+clean:
+	@rm -f *~ *.aux *.log *.bak *.out *.toc *.dvi *.ps
+
+archclean: clean
+	@rm -f *.pdf
+
+single:
+	pdflatex manual
+
+manual.pdf: preface.tex background.tex defect-reporting.tex howtos.tex manual.tex qa.tex burning-compatibility.tex download.tex local.tex overview.tex
+	pdflatex manual
+	pdflatex manual
+	pdflatex manual

documentation/user-manual/background.tex

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+\section{Background information}
+\label{background}
+
+The information in this sub section is not required for operating 
+dvdisaster. However it is helpful for understanding how dvdisaster works 
+and may help you getting the most out of the program according to your needs. 
+
+\subsection{Properties of the error correction}
+\label{background-properties}
+
+This sub section outlines the basic ideas behind dvdisaster so that you can 
+see for yourself whether it meets your demands on data safety. If in doubt, 
+you should not use dvdisaster as a single means of protecting your data
+and deploy additional data backup strategies.
+
+\paragraph{Method of error correction.}   dvdisaster 
+uses a \href{http://en.wikipedia.org/wiki/Reed-Solomon_error_correction}{Reed-Solomon code } together 
+with an error correction algorithm optimized for the treatment of erasures. The 
+implementation draws a lot of inspiration and program code from the 
+excellent \href{http://www.ka9q.net/code/fec/}{Reed-Solomon} library written 
+\href{http://www.ka9q.net/}{by Phil Karn}.
+
+Using the \tlnk{howto-eccfile-basic-settings-ecc}{standard settings} of 
+an \tlnk{howto-eccfile}{error correction} file 223 medium sectors 
+are combined into one error correction code (``ECC'') block. 
+Medium read errors are regarded as ``erasures''; therefore a maximum 
+of 32 bad medium sectors\footnote{The given threshold of 32 correctable errors per ECC 
+block is the standard setting. It is possible to select \tlnk{howto-eccfile-basic-settings-ecc}{other values} 
+for higher or lower error correction capabilities. 
+When \tlnk{howto-augment}{error correction data is put directly on the medium}, 
+the number of correctable errors depends on the free space on the medium.} are 
+correctable per ECC block.
+
+The 223 sectors are selected so that they are evenly distributed over the medium 
+surface. Therefore large contigous areas of defective sectors can be corrected before 
+the threshold of 32 defects per ECC block is reached. This kind of error 
+pattern is especially common for an aging medium where the outer area is starting 
+to degenerate, and for scratches along the data spiral.
+
+On the other hand, radial or diagonal scratches are expected to be correctable 
+in the optical disc drive itself. If not, the employed error correction 
+strategy performs rather neutral in these cases (neither especially good 
+nor extraordinary bad).
+
+\paragraph{Limits of error correction.} In the wost case, 33 defective sectors (for the
+standard setting) are sufficient to prevent a full data restoration. However 
+to achieve this effect, the errors have to be distributed over the medium in such 
+a way that they occur in the same ECC block - such patterns are very unlikely.
+Empirical tests have shown that on aging media about 10\% of the overall 
+sector count may become defective before the threshold of 33 defects per ECC block is reached.
+Scratches will cause the threshold to be reached earlier, therefore it is 
+recommended to visually check the media in regular intervals. Media with read errors 
+caused by scratches should be replaced immediately.
+
+\paragraph{Hardware limits.}  Most drives will not recognize media when the 
+lead-in area before the first sector (near the center hole) is damaged. 
+In such cases, dvdisaster will not be able to recover any content from the media.
+
+It is not feasible to enhance the reliability of poor quality media by using 
+dvdisaster. Cheap media can decay within a few days to an extent which will 
+exceed the capabilities of the error correction code. 
+
+\subsection{Image level data recovery}
+\label{background-image-level}
+
+Media recovery with error correcting codes takes place in two steps:
+
+\begin{enumerate}
+\item First as much data as possible is read from the defective medium.
+\item Then the still missing data is recovered using the error correction code.
+\end{enumerate}
+
+The amount of readable data (step 1) does not only depend on the reading 
+capabilities of the drive, but also on which logical level the reading process 
+takes place. This page discusses the logical levels and explains why dvdisaster 
+uses image level reading. Please see also \tlnk{qa-image-level}{Q1.5} for
+a visualization of this concept.
+
+\paragraph{Logical levels of a medium.} Optical discs are organized into 
+{\em data sectors} containing 2048 bytes each. Consecutively reading and storing 
+these sectors produces a medium {\em image}.
+
+But working with single data sectors is unwieldy from a users perspective. Therefore 
+media contain {\em file systems} which combine data sectors into {\em files}. 
+This requires accurate book-keeping about which data sectors each file is 
+comprised of, and also further attributes like file names and access permissions. 
+For this book-keeping some data sectors are reserved on the medium and filled 
+with respective data structures.
+
+As a consequence media contain different {\em logical levels}: Viewing the 
+medium as a sequence of data sectors means working at the {\em image level}. 
+However looking at the medium as a collection of files is the perspective of 
+the {\em file(system) level}.
+
+\smallskip
+
+The two levels have different properties when it comes to data recovery:
+
+\paragraph{Shortcomings of reading a medium at the file level.} Reading a defective 
+medium at the file level means trying to read as much data as possible from each file.
+
+But a problem arises when data sectors are damaged which have book-keeping 
+functions in the file system. The list of files on the medium may be truncated. 
+Or the mapping of data sectors to files is incomplete. Therefore files or parts 
+from files may be lost even though the respective data sectors would still 
+be readable by the hardware. This is very bad since even small readable portions 
+of damaged files are valuable for the error correcting code.
+
+An extremely bad case occurs when the error correction data is also stored in 
+files. Then the error correction data is required to repair the file system, 
+but the defective file system prevents access to the error correction data. 
+That means total data loss and rises some issues on 
+the treatment of error correction files (more on that later in this sub section).
+
+A similar problem arises when files are augmented with PAR2 error correction 
+data and then all these files are stored on the same medium. If the internal 
+bookkeeping of the file system becomes damaged, all files and therefore the 
+error correction data become inaccessible and are therefore lost.
+
+\smallskip
+
+However the situation improves greatly when employing an image-based approach:
+
+\paragraph{Advantages of reading at the image level.} Reading at the image level 
+uses direct communication with the drive firmware to access the data sectors.
+
+The number of readable sectors depends only on the reading capabilities of the drive, 
+but not on the state of the file system. A read error in one sector does not 
+block access to other data sectors. Since {\em all} sectors are recovered 
+which are still readable by the hardware, this method provides the best foundation 
+for the error correction.
+
+Another consideration is that the image contains all data sectors of 
+the medium. When the image is completely 
+recovered the file system stored within is also fully repaired. A protection 
+at the image level is therefore more extensive than error correction at the file level.
+
+dvdisaster is working exclusively at the image level to take advantage of these properties. 
+The \tlnk{background-methods}{RS02 and RS03 methods} even allow 
+for \tlnk{howto-augment}{storing the error correction data at the same medium}. 
+This is possible since reading the error correction information at the image level 
+can not be blocked by errors at other medium locations (damaged sectors with error 
+correction data will reduce the error recovering capacity, but not make recovery impossible).
+
+\smallskip
+
+The \tlnk{background-methods}{RS01 method} protects media at the image level, too, 
+but stores the error correction data in files. The next section hints at some pitfalls 
+arising from that.
+
+\paragraph{Consequences for error correction file storage.} \label{background-image-level-consequences}The error correction data 
+created by dvdisaster protects media at the image level. But how are the error correction 
+files protected?
+
+\smallskip
+
+Since error correction files are read at the file level they are subject to the 
+problems discussed above. If the medium containing the error correction files 
+becomes damaged it may not be possible to access or read them completely.
+
+Therefore it is important to protect error correction files at the image level as 
+well: \tlnk{background-eccfile-storage}{Media containing error correction files} must be 
+protected with dvdisaster, too.
+
+Since image level protection is assumed there is {\em no further damage protection}
+contained in the RS01 error correction files! This would not help much, anyways: 
+Error correction files could be created in a way that allows them to provide a 
+reduced data recovering capacity even when being damaged\footnote{Error correction files 
+created with the new RS03 codec have exactly these properties, e.g. they are robust 
+against damage as long as there is enough error correction capacity left. This is 
+possible as there is sufficient computing power and fast hard drive access available 
+now to create a suitable file format. At the time RS01 was developed these resources 
+were not yet available. But it must be stressed that even for RS03 error correction 
+files the disadvantages of reading at the file level hold!}. But 
+however such internal protection would be designed, the error correction file would 
+still be only protected at the file system level with all the disadvantages discussed above!
+
+In addition, the computing time and redundancy used for internal protection is 
+better spent at the image level: The Reed-Solomon error correction works best
+ when error correction information is spread over huge amounts of data. It is 
+better to protect the image as a whole than individually protecting each file within.
+
+ 
+\subsection{The RS01, RS02 and RS03 methods}
+\label{background-methods}
+
+dvdisaster contains three error correction methods.
+RS01 and RS02 have been available right from the start of the project.
+RS03 has been added recently to take advantage of 
+recent hardware, and to implement improvements
+learned from evaluating its predecessors.
+
+\paragraph{Comparison of the methods.} All three methods build on the 
+same \tlnk{background-properties}{Reed-Solomon} error correction. They calculate error 
+correction information for ISO images which is used to recover unreadable sectors if 
+the disc becomes damaged afterwards.
+
+\smallskip
+
+The methods differ in the way the error correction information is stored:
+
+\begin{itemize}
+\item  RS01 creates {\bf error correction files} which are stored separately 
+from the image they belong to. Since data protection at 
+the \tlnk{background-image-level}{file level} is difficult, 
+error correction files must be stored on media which are protected against data loss by dvdisaster, too.
+
+\item To apply the RS02 method an image is first created on hard disk using a 
+optical disc authoring (or writing) software. Before the image is written on the medium, 
+dvdisaster is used to {\bf augment the image} with error correction data. 
+Therefore the data to be protected and the error correction information are located at 
+the same medium. Damaged sectors in the error correction information reduce the data recovering 
+capacity, but do not make recovery impossible - a second medium for keeping or protecting the 
+error correction information is not required.
+\end{itemize}
+
+
+RS03 is a further development of RS01 and RS02. 
+It can create both error correction files and augmented images:
+
+\begin{itemize}
+\item RS03 can distribute work over multiple processor cores and is 
+therefore much faster than RS01/RS02 on modern hardware.
+\item RS03 {\bf error correction files} are - contrary to RS01 - robust 
+against damage. This should not delude you into careless handling of your error 
+correction files though - the disadvantages of \tlnk{background-image-level}{reading at the filesystem level} are 
+still valid.
+\item RS03 {\bf augmented images} do not require so-called master blocks 
+holding important information. This makes RS03 a bit more robust, but also more restrictive: 
+The augmented image must completely fill the medium now while the size of augmented images 
+can be freely chosen in RS02.
+\end{itemize}
+
+The changes for parallel computation and higher robustness make RS03 a bit less space efficient, 
+e.g. RS03 error correction data has slighly less error correction capacity than 
+its RS01/RS02 counterparts on images with equal size.
+
+\newpage
+
+\paragraph{Comparison of error correction storage.} The following table summarizes the differences 
+between error correction files (RS01, RS03) and augmented images (RS02, RS03):
+
+\smallskip
+
+\begin{tabular}{|p{0.473\textwidth}|p{0.473\textwidth}|}
+\hline
+{\em Error correction files} 	& 
+{\em Image augmented with error correction data} \\
+\hline
+any possible redundancy can be chosen &	
+redundancy is limited by free space on the medium (= medium capacity - size of data image) \\
+\hline
+already effective at 15\% redundancy since error correction files are required to be free of damage &
+requires more redundancy (recommended: 20-30\%) to compensate defects in the error correction data \\
+\hline
+medium can be completely filled with data  &
+usable medium capacity is reduced by amount of error correction data \\
+\hline
+can be created for already existing media & 
+only applicable before writing the new medium since the image must be augmented with error correction information in advance \\
+\hline
+separately storing the error correction file from user data strengthens data protection &
+common storage of user data and error correction data may reduce error correction capacity \\
+\hline
+mapping between error correction files and media must be kept; error correction files must be 
+protected against damage &
+easy one-medium solution; error correction information needs not to be cataloged or explicitly protected \\
+\hline
+no compatibility issues with play-back units &
+media with augmented images may not play correctly on all units \\
+\hline
+\end{tabular}
+
+\paragraph{Further reading.} The specification for the dvdisaster codecs 
+has been specified in a separate document called \href{http://dvdisaster.net/downloads/codecs.pdf}{codecs.pdf}. 
+Good knowledge in coding theory and programming is required.
+
+\subsection{The linear reading strategy}
+\label{background-linear}
+
+dvdisaster contains two different reading strategies.
+
+\medskip
+
+{\bf The linear reading strategy is recommended for:}
+
+\begin{itemize}
+\item Creating images from undamaged media,
+  e.g. to \tlnk{howto-eccfile}{generate the error correction file}; and
+\item \tlnk{howto-scan}{Scanning the medium} for reading speed and read errors.
+\end{itemize}
+
+\medskip
+
+{\bf The} \tlnk{background-adaptive}{adaptive reading strategy} {\bf is recommended for:}
+
+\begin{itemize}
+\item \tlnk{howto-recover}{Extracting data from damaged media.}
+\end{itemize}
+
+\paragraph{Properties of the linear reading strategy.}\quad
+
+\medskip
+
+Optical media are
+organized into sectors which are continously numbered beginning with zero.
+Each sector contains 2048 bytes of data.
+
+\begin{figure}
+\centerline{\includegraphics[width=1.0\textwidth]{screenshots/weak-cd-scan.png}}
+\caption{Linear reading of a weak but fully readable CD.}  
+\label{background-linear-weak-scan}
+\end{figure}
+
+The linear reading strategy reads the medium from the start (sector 0)
+until the end (last sector). The reading speed is shown graphically to
+provide information about the medium quality (see
+figure \ref{background-linear-weak-scan} for an example and the explanations
+in the following paragraphs). 
+
+\paragraph{Configuration.}\quad
+
+\medskip
+
+\paragraph{Number of sectors to skip after a read error.} Reading
+attempts for defective sectors are slow and may wear out the drive
+mechanics under unfavourable conditions. A series of read errors,
+spread over a continous sector range, is more common than single spot defects.
+Therefore a \tlnk{howto-scan-prefs-read-attempts}{configuration option} exists
+so that a certain number of sectors
+will be skipped after the occurance of a read error. The skipped sectors are
+assumed to be defective without further reading attempts. Some guide lines for
+selecting the number of skipped sectors are:
+
+\begin{itemize}
+\item Skipping a large number of sectors (e.g. {\bf 1024}) gives a quick
+  overview of the degree of damage, but will usually not collect enough
+  data for repairing the medium image.
+\item Smaller values like {\bf 16, 32 or 64} are a good trade-off: The processing
+  time will be considerably shortened, but still enough data for repairing
+  the image is usually collected.
+\item On DVD and BD  media read errors do usually extend over at least 16 sectors
+  for technical reasons. Therefore a sector skip less than 16 is not recommended
+  for such  media.
+\end{itemize}
+
+\paragraph{Limiting the reading range.}
+
+\medskip
+
+Reading can
+be \tlnk{howto-scan-prefs-image}{limited to a given range of sectors} in
+the ``Image'' preferences tab. This is helpful during
+multiple read attempts of damaged media. 
+
+\paragraph{Estimating media quality.}\quad
+
+\medskip
+
+\paragraph{The speed curve.} Most drives
+will slow down while reading medium areas which are in bad condition:
+
+\begin{itemize}
+\item Drops in the reading speed can be a warning for an imminent medium failure.
+\item However some drives will read with full speed until the bitter end.
+  With such drives media deterioration may not show up in the reading
+  curve until actual read errors occur.
+\end{itemize}
+
+  The reading curve is most accurate when using
+  the ``\tlnk{howto-scan}{Scan}'' function.
+  During the ``\tlnk{howto-eccfile-create}{Read}'' operation the
+  read data will be written to the hard
+  drive at the same time, which may cause irregularities in the reading curve
+  depending on the operating system and hardware used.
+
+\paragraph{Read errors.} Read errors cause \tlnk{howto-interpret-defective-cd}{red markings} in
+the spiral or respective messages at the command line. This means
+that the medium could not be read at these places during the current reading pass:
+
+\begin{itemize}
+\item The medium is most likely defective.
+\item The image should be \tlnk{howto-recover}{repaired} as
+  soon as possible and then be transferred to a new medium.
+\end{itemize}
+
+\subsection{The adaptive reading strategy}
+\label{background-adaptive}
+
+Please note: Adaptive reading is unavailable in the current
+version of dvdisaster as it requires rework for RS03. It
+will be re-introuced soon. It is documented here for completeness:
+%dvdisaster contains two different reading strategies.
+
+\medskip
+
+{\bf The adaptive reading strategy is recommended for:}
+
+\begin{itemize}
+\item \tlnk{howto-recover-read}{Extracting data} from damaged media,
+\end{itemize}
+
+\medskip
+
+{\bf The} \tlnk{background-linear}{linear reading strategy} {\bf is recommended for:}
+
+\begin{itemize}
+\item \tlnk{howto-eccfile-create}{Creating images} from undamaged media,
+  e.g. to generate the error correction file.
+\item \tlnk{howto-scan}{Scanning the medium} for reading speed and read errors.
+\end{itemize}
+
+\paragraph{Properties of the adaptive reading strategy.}\quad
+\medskip
+
+The adaptive reading strategy uses a ``divide and conquer'' approach for locating still readable portions of a damaged medium. The strategy is based upon an article published by Harald Bögeholz in c't-Magazin 16/2005 where it was published together with the program {\em h2cdimage}:
+
+\begin{enumerate}
+\item At the beginning the medium is considered as a single unread interval.
+  Reading begins with sector zero.
+\item The reading process continues sequentially unless either the end of the
+  current interval or a read error is encountered.
+\item The reading process is terminated if either (3a) sufficient sectors for
+  a successful error correction have been read or (3b) no unreadable intervals
+  exceeding a given size remain.
+\item Otherwise the largest remaining unread interval will be determined. Reading
+  continues in the middle (e.g. second half) of this interval; the first half of
+  this interval is kept for a later reading pass.
+\end{enumerate}
+
+\begin{figure}
+\centerline{\includegraphics[width=1.0\textwidth]{screenshots/adaptive-progress.png}}
+\caption{Progress of th adaptive reading.}  
+\label{background-adaptive-progress}
+\end{figure}
+
+The termination criterium (3a) is especially efficient: Reading
+will stop as soon as enough sectors have been collected for a
+successful image recovery using the error correction file. This
+can reduce the reading time by as much as 90 percent compared
+with a full read attempt, but does of course only work when
+error correction data is available.
+
+\paragraph{Configuration}\quad
+
+\medskip
+
+\paragraph{Error correction file.} Adaptive reading works best when error
+correction data is available. Obviously the \tlnk{howto-ecc}{error correction data} must have
+been created at a time where the medium was
+still fully readable. To use a \tlnk{howto-eccfile-create}{error correction file} during 
+adaptive reading,
+\tlnk{howto-recover-enter-eccfile}{enter its name} before starting the reading process.
+
+\paragraph{Limiting the adaptive reading range.} Reading can
+be \tlnk{howto-eccfile-prefs-image}{limited} using the ``Image'' preferences
+to a part of the medium. This is not recommended
+when error correction data is used since the limit might prevent sectors
+from being read which are required for a succesful error correction. If
+no error correction data is available, limiting the reading range might
+be helpful during multiple reading attempts.
+
+\paragraph{Early reading termination.} If no error correction
+data is available, adaptive reading will stop when no unread intervals
+\tlnk{howto-recover-prefs-read-attempts}{larger than a selectable size} remain.
+
+The termination value should not be smaller than 128. Otherwise the laser
+head will have to carry out lots of repositioning moves during the final
+phase of the reading process. This will negatively affect both the life
+expectancy of the drive and its reading capability. A better approach is
+to stop adaptive reading earlier and then try reading the remaining sectors
+with an additional \tlnk{background-linear}{linear reading} pass. 
+
+\subsection{Remarks on read errors}
+\label{background-read-errors}
+
+Optical media have their own error correction code which protects the data against
+small manufacturing errors and inaccuracies during writing. If the writer and medium
+are compatible and of high quality, the error correction built into the medium will
+at first be mainly idle. This leaves enough reserves to compensate normal wear and
+aging effects during many years of the medium usage.
+
+\smallskip
+
+When the capacity of the built-in error correction is finally exhausted, read errors
+will start to appear on the medium. These will be reported by
+the ``\tlnk{howto-scan}{Scan}''-operation
+of dvdisaster. Depending on the time of first occurrence, two types of read errors
+are of particular interest:
+
+\paragraph{Read errors appearing right after writing the medium.} This is a sign of:
+
+\begin{itemize}
+\item media from a faulty production run, or
+\item media which are not compatible with the writer.
+\end{itemize}
+
+A prudential choice is to dispose of the faulty media and to write the data
+on error-free media, possibly switching to a different producer.
+
+\smallskip
+
+Please withstand the temptation of trying to preserve the faulty media
+by means of an error correction file - this will most likely end with data loss.
+
+\paragraph{Read errors after a few months/years.} The built-in error correction
+of the medium will be increasingly loaded during its life time until it finally
+fails and read errors show up. This happens for mechanical reasons (scratches,
+warping of the plastic material) as well as for chemical causes (decaying dye
+and/or reflective layer).
+
+\smallskip
+
+These effects typically occur while the medium is stored away for a few months,
+and it may not be possible to read in all sectors afterwards.
+
+\smallskip
+
+Therefore it is crucial to \tlnk{howto-ecc}{create the error correction data} in
+time. The ecc data contains information for recalculating the contents of missing
+sectors (\tlnk{background-properties}{within certain limits}).
+Therefore with the help of the ecc data dvdisaster can recover images even
+if not all sectors could actually be read by the drive.
+
+\smallskip
+
+Since the error correction can reconstruct missing sectors up to a certain number,
+it is not necessary to squeeze out a defective medium for every readable sector.
+The \tlnk{background-adaptive}{adaptive reading strategy} checks during reading
+whether enough data for error correction has been collected. As soon as this is
+the case, reading stops and still unread sectors will be recovered using the ecc data.
+
+\paragraph{Some hints for effectively reading damaged media}\quad
+
+\medskip
+
+The outcome from reading damaged media depends on several factors:
+
+\begin{itemize}
+\item {\bf Not all drives are built the same.}
+  
+  Different drives have different reading capabilities. Take advantage of dvdisaster's
+  function for completing an image with several reading passes and use different drives
+  for each pass. Transfer the image file between computers using a network or removable
+  media in order to use drives installed in different machines.
+
+\item {\bf Eject and insert the medium again.}
+  
+  Sometimes it makes a difference to eject the medium, turn it about a quarter,
+  and then load it again for another reading pass.
+
+  \item {\bf Some drives read better while being cold.}
+
+    Turn off the computer over night and perform another reading attempt in the next morning.
+
+    But note: ``Cold'' refers to normal living room conditions - putting hardware or
+    media into the fridge can be very unhealthy for them.
+ \end{itemize}
+
+
+\subsection{Hints for storing the error correction files}
+\label{background-eccfile-storage}
+
+Currently there are few (if any) exchangeable media technologies which can be a
+cost-effective alternative to the various optical disc formats. So you will
+probably not only use optical discs for data archival, but store the respective
+error correction files on CD, DVD or BD as well.
+
+\smallskip
+
+There is nothing wrong with that, but bear in mind that your archived data and
+the error correction files are stored on media with the same degree of reliability.
+When read errors occur on the archived data, be prepared that the disc with the
+respective error correction file might have aged beyond full readability, too.
+
+\smallskip
+
+Therefore it is important to protect your error correction files with the same
+care as your other data\footnote{You might also choose
+  an \tlnk{howto-augment}{augmented image} using RS02 or RS03 instead
+  of creating an error correction file.}.
+This is best achieved by integrating the error correction files into
+your normal data backup scheme. Here are two ideas:
+
+\paragraph{1. Storing the error correction files on dedicated media:}\quad
+\medskip
+
+If you decide to store error correction files on separate media, it
+is \tlnk{background-image-level-consequences}{important} to protect those media
+with dvdisaster as well. To avoid a never-ending chain (error correction
+files for media of error correction files for ...), try the following:
+
+\smallskip
+
+Lets assume that five error correction files can be stored at each medium.
+Write the first five error correction files to the first medium and create
+another error correction file for that medium. Now save that error correction
+file together with four other error correction files on the second medium.
+If you continue that way, all error correction files except for those from the
+last medium (which may still be kept on hard disk) are protected by dvdisaster.
+
+\paragraph{2. Putting the error correction file on the next medium of a series:}\quad
+\medskip
+
+If you do not fill your media to the max (e.g. with less than 4GiB for
+a single layered DVD), you can store the error correction file of one
+medium on the succeeding medium within a series.
+
+ 

documentation/user-manual/burning-compatibility.tex

@@ -0,0 +1,196 @@
+\section{Burning software compatibility}
+\label{burning-compatibility}
+
+dvdisaster must be used in conjunction with a CD/DVD/BD writing suite (``burning program'')
+in order to generate ISO images and to write augmented ISO image files. Unfortunately,
+not all burning programs provide the required features to work with dvdisaster.
+Some burning programs may even produce media and/or ISO images which can not be
+used with dvdisaster.
+
+\smallskip
+
+For your convenience, the dvdisaster project has tested some free burning programs
+available for GNU/Linux. Please note that this list will always be incomplete and
+only be a snapshot of a certain program version. It is likely to be outdated when
+you are reading this page. It is therefore recommended that you test your specific
+burning program version by following the \tlnk{howto-compat-overview}{instructions} given
+in the howto section.
+
+\paragraph{Recommended software}\quad
+
+\medskip
+
+The dvdisaster project recommends either using the command line tools
+listed below or using the K3B burning application (which is actually
+a graphical wrapper around the command line tools).
+
+\paragraph{Burning program compatibility table}\quad
+
+\medskip
+
+\newcommand{\tgrey}[1]{\cellcolor{dkgrey}#1}
+\newcommand{\tturquoise}[1]{\cellcolor{turquoise}#1}
+\newcommand{\tpink}[1]{\cellcolor{pink}#1}
+\newcommand{\tblue}[1]{\cellcolor{dkblue}#1}
+
+\newcommand{\tred}[1]{&\begin{minipage}{10mm}{\cellcolor{ltred}#1}\end{minipage}}
+\newcommand{\tyellow}[1]{&\begin{minipage}{10mm}\cellcolor{ltyellow}{#1}\end{minipage}}
+\newcommand{\ok}{&\cellcolor{ltgreen}OK}
+\newcommand{\na}{&\cellcolor{ltgrey}n.a.}
+\newcommand{\nt}{&\begin{minipage}{10mm}{not tested}\end{minipage}}
+
+\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|}
+\hline
+\tgrey{} & \tgrey{} & \tgrey{} & \tturquoise{Create} &
+  \multicolumn{3}{c|}{\tpink{Burning images}} & \multicolumn{3}{c|}{\tblue{Burning images}} \\
+  
+  \tgrey{Program} & \tgrey{Version} & \tgrey{Testing} & \tturquoise{ISO/} &
+  \multicolumn{3}{c|}{\tpink{for error}} &
+  \multicolumn{3}{c|}{\tblue{with embedded}} \\
+
+\tgrey{} & \tgrey{} & \tgrey{Date} & \tturquoise{UDF} & 
+  \multicolumn{3}{c|}{\tpink{correction files}} &
+  \multicolumn{3}{c|}{\tblue{error correction}} \\
+  
+  \cline{5-10}
+\tgrey{} & \tgrey{} & \tgrey{} &\tturquoise{Image} &\tpink{CD} &\tpink{DVD} &\tpink{BD} &\tblue{CD} &\tblue{DVD} &\tblue{BD} \\
+
+  \hline
+  \multicolumn{10}{|c|}{\cellcolor{ltgrey}Command line tools} \\
+  
+  \hline
+  genisoimage & 1.1.11 & Jul'14        \ok \na \na \na \na \na \na \\
+
+  \hline
+  wodim       & 1.1.11 & Jul'14        \na \ok \ok \na \ok \ok \na \\
+
+  \hline
+  growisofs   & 7.1    & Jul'14        \na \na \ok \ok \na \ok \ok \\
+
+  \hline
+  \multicolumn{10}{|c|}{\cellcolor{ltgrey}Tools with a graphical user interface} \\
+
+  \hline
+  brasero     & 3.4.1 & Jul'14         \tred{no UDF$^{1)}$} \tyellow{avoid$^{2)}$} \ok \na \tyellow{avoid$^{2)}$} \ok \na \\ 
+
+  \hline
+  K3B         & 2.0.2 & Jul'14         \ok \ok \ok \na \ok \ok \na \\
+
+  \hline
+  xfburn      & 0.4.3 & Jul'14         \ok \tyellow{re-read only$^{3)}$} \tyellow{re-read only$^{3)}$} \na \tred{do not use$^{3)}$} \tred{do not use$^{3)}$} \na \\
+  \hline
+\end{tabular}
+
+\bigskip
+
+\paragraph{Testing conditions and objectives}\quad
+\medskip
+
+Testing was done using Debian 7.5 (wheezy) on an amd64 machine.
+Versions of the tested writing software are indicated in the table above.
+
+\medskip
+
+Evaluation of the burning software is done for the two major cases where
+interoperability with dvdisaster is required: 
+
+\bigskip
+
+a) Creating error correction files
+
+\medskip
+
+The burning program is used to assemble an ISO image from a selected set of files,
+and to write a CD, DVD or BD disc from it. An \tlnk{howto-eccfile}{error correction file} will
+be created to protect this medium.
+
+\smallskip
+
+There are two ways of obtaining the ISO image for creating the error correction file:
+
+\begin{enumerate}
+\item The burning program is used to create an ISO image which is stored on hard disk.
+  This image is used for burning the medium and for creating the error correction file.
+  If the writing software creates a medium which does not exactly match the image,
+  the resulting error correction file may be useless.
+  A respective \tlnk{howto-compat-file}{testing method} is described
+  in the ``Howtos'' section. An ``OK'' in the table above indicates that
+  this test has been passed. But you are strongly advised to
+  \tlnk{howto-compat-file}{do your own test} at least
+  once to make sure that you are working on the same versions and premises.
+
+  \smallskip
+  
+  If it is not possible to use a pre-made ISO image for both writing the medium
+  and for creating the error correction file, the writing software is
+  rated ``Re-read only'' in the table. In that case, use the alternative
+  approach described below (topic 2).
+
+\item The burning program is used to write a medium, either by using a
+  pre-made ISO image or by creating the image on-the-fly while writing
+  the medium. Afterwards, the pre-made ISO image is discarded. dvdisaster
+  is used to read back a new ISO image from the newly written medium. From
+  this newly created ISO image the error correction file is created. This
+  process should always work; if not, the respective burning software is
+  marked as being unusable in the table.
+\end{enumerate}
+  
+\bigskip
+
+b) Augmenting a medium with error correction data
+
+\medskip
+
+\tlnk{howto-augment-write-iso}{Creating a medium}
+\tlnk{howto-augment}{with embedded error correction data} is comprised of
+several sub tasks: First, the burning application converts a selection of files
+into an ISO image stored on hard disk. dvdisaster augments the image residing
+on the hard disk with error correction data. Then, the burning application
+writes the augmented image to the CD, DVD or BD. The ISO image content or format
+must not be altered during the writing process. Especially, the added error correction
+sectors must not be removed and no padding sectors must be added to the image during
+the writing process. The ``Howto'' section describes
+\tlnk{howto-compat-augment}{a test for compatibility between
+a writing software and dvdisaster}. An ``OK'' in the table above indicates that this
+test has been passed; otherwise you can not use the respective software for writing
+augmented images. You are strongly advised to \tlnk{howto-compat-augment}{do your own test} at
+least once to make sure that you are working on the same versions
+and premises even with software marked as compatible in the table above.
+
+\bigskip
+
+c) Creating ISO images
+
+\medskip
+
+In addition, the table indicates whether the burning application can convert
+a selection of files into an ISO image and store that ISO image on hard disk
+for further processing with dvdisaster. 
+
+\paragraph{Notes (why a certain software failed a test)}\quad
+\medskip
+
+$^{1)}${\bf brasero} can only create ISO images, not ISO/UDF. This is not
+recommended for DVD-Video authoring and has the disadvantage that files
+with sizes greater than 2GiB can not be used in a portable way (the tested
+version can not use files larger than 2GiB at all even if it says otherwise).
+
+\bigskip
+
+$^{2)}${\bf brasero} does not support the ``disc at once'' writing strategy. This
+creates two spurious unreadable sectors at the end of CD media. dvdisaster
+can handle such media, but will issue a warning and requires a preferences
+setting each time such media is processed.
+
+\bigskip
+
+$^{3)}${\bf xfburn} can not be used to write RS02/RS03 augmented images due to a
+wrong implementation of padding sector handling. In a correct implementation,
+a burning program would add 150 zero padding sectors to an image it has created
+itself. However padding sectors must never be added to an image which was created
+or manipulated by a foreign application, such as an image being augmented by dvdisaster.
+This results in the image being read back with wrong checksums, and dvdisaster will
+rightfully complain that the ``Image file is 150 sectors longer than expected.''.
+Error correction files can - for the same reason - not be used when created from
+the original image, but it is possible to re-read the image from the written
+medium and create error correction files from that image. 

documentation/user-manual/defect-reporting.tex

@@ -0,0 +1,67 @@
+\section{Reporting defects (aka bugs)}
+\label{reporting-defects}
+
+Like all complex software, dvdisaster may contain defects (programming errors) and
+incompatibilities with certain (drive) hardware and software setups. You are invited
+to tell us about any difficulties you encounter with the program or the documentation
+so that we can improve things in future releases.
+
+To make sure that we are getting the right information, we have provided the
+following checklist for defect reporting.
+
+\paragraph{Please check first that you are really experiencing a defect:}\quad
+\medskip
+
+\begin{itemize}
+\item Make sure that you are using the latest genuine version from
+  our \tlnk{download}{download site}. dvdisaster versions provided
+  by third parties may contain functions and defects which are not present
+  in the original version (and we can't fix problems introduced by third parties).
+
+  Please do also note that the dvdisaster project does no longer
+  make and publish versions for the Windows and Mac OS operating
+  systems. Reported defects for those platforms will not be processed.
+
+\item Double check that the issue you have encountered is not already
+  covered in the \tlnk{qa}{Questions and Answers} section.
+\item Please note that dvdisaster will only work with the (re-)writeable varieties
+  of media, so seeing it {\bf reject DVD-ROM and BD-ROM} is not an error.
+  Also, CD-Audio, VCD, SVCD and multisession CD are not supported as well as
+  all HD-DVD formats (\tlnk{qa-technical-media}{complete list of supported media formats}).
+\item dvdisaster works only with real optical drives. Not supported are
+  network drives, software drives (e.g. alcohol) and drives in virtual machines.
+\end{itemize}
+
+\paragraph{How to report issues with the program:}\quad
+\medskip
+
+Please report your findings by sending an email to {\em carsten@dvdisaster.org}.
+Your report should contain:
+
+\begin{itemize}
+\item Information about the operating system and dvdisaster version you are using;
+\item the drive and media type(s) which exhibited the problem;
+\item a textual description of the issue you encountered;
+\item a screen shot of the error message and/or output which might provide further information about the problem;
+\item differences between working and non-working configurations if the issue is experienced only on certain drives/computers;
+\item a log file if you suspect that the issue is related to a drive or medium incompatibility.
+\end{itemize}
+
+\paragraph{How to create a log file:}\quad
+\label{reporting-defects-log}
+\medskip
+
+\begin{figure}[h]
+\centerline{\includegraphics[width=\textwidth]{screenshots/activate-logfile.png}}
+\caption{Creating a log file.}  
+\label{defect-prefs-log}
+\end{figure}
+
+If you suspect incompatibilities with your drive and/or media as the cause of your
+issue, please activate the log file feature in the preferences dialog as shown in
+the screen shot. Then perform a scanning or reading action and attach the log file
+to your bug report.
+
+\bigskip
+
+Thanks for your feedback!

documentation/user-manual/download.tex

@@ -0,0 +1,138 @@
+\section{Downloading dvdisaster}
+\label{download}
+
+\begin{tabular}{ll}
+\hspace*{-2mm}\begin{minipage}{122mm}
+dvdisaster is available for \tlnk{download-requirements}{recent versions} of the FreeBSD,
+GNU/Linux and NetBSD operating systems. It is provided
+as \href{http://fsfe.org/about/basics/freesoftware.en.html}{free Software} under
+the \href{http://www.gnu.org/licenses/gpl-3.0.txt}{GNU General Public License v3}.
+\end{minipage} &
+\begin{minipage}{34mm}
+\includegraphics[width=34mm]{icons/gplv3-127x51.png}
+\end{minipage}
+\end{tabular}
+
+\bigskip
+
+The dvdisaster developer site (\url{http://dvdisaster.net}) contains
+the latest source code releases for the FreeBSD, GNU/Linux and NetBSD
+operating systems. These are mostly aimed at maintainers of binary packages for
+the beforementioned platforms. As an end user you might find it more convenient
+to install dvdisaster from the package system of your operating system bundle or
+distribution. But if you prefer to download and compile the source package on your
+own, you're welcome to visit the site.
+
+\bigskip
+
+The source code archives contain a file {\tt INSTALL} with further instructions
+for building dvdisaster. The build process follows the 
+common {\tt ./configure; make; make install} scheme. The installation step
+is optional; you can use dvdisaster directly from the build tree.
+
+\subsection{System requirements}
+\label{download-requirements}
+
+\paragraph{Hardware requirements}\quad
+
+\begin{itemize}
+\item x86, PowerPC or Sparc processor;
+\item an up-to-date CD/DVD/BD drive with ATAPI, SATA or SCSI interface;
+\item enough hard disk space for creating .iso images from processed media.
+\end{itemize}
+
+\bigskip
+
+{\bf Supported operating systems}\quad
+
+\medskip
+
+The following table gives an overview of the supported operating systems.
+The specified releases have been used for developing and testing the
+dvdisaster version made available as of this writing. 
+Typically, slightly older and newer OS versions will also work.
+\label{download-requirements-freebsd}
+
+\bigskip
+
+\begin{tabular}{|l|l|}
+\hline
+Operating System & Release \\
+\hline
+GNU/Linux & Debian Jessie 8.0,  Kernel 3.16 \\
+\hline
+FreeBSD & 10.1 \\
+\hline
+NetBSD & 6.1.5 \\
+\hline
+\end{tabular}
+
+\bigskip
+
+\paragraph{Not supported operating systems}\quad
+
+\medskip
+
+Support for Windows and Mac OS has been ended
+and is not planned to be resumed in the
+future (see \tlnk{qa-discontinued-os}{QA item 2.4 for an explanation)}. 
+
+\newpage
+\subsection{Make sure you're not getting ripped off: The small print (and other things).}
+\label{download-terms}
+
+The dvdisaster project provides this software
+as \href{http://fsfe.org/about/basics/freesoftware.en.html}{free software} to you using
+the \href{http://www.gnu.org/licenses/gpl-3.0.txt}{GNU General Public License v3}.
+The dvdisaster project also wants to make sure that you know you can download
+the software at no cost and keeping your full privacy.
+To make it clear how we distribute dvdisaster, what we do and what we
+won't do, we have compiled the following list:
+
+\paragraph{Internet and download sites}\quad
+
+\smallskip
+
+The dvdisaster project uses the following internet domains for publishing
+its web sites and supplying software downloads:
+
+\begin{center}
+  \begin{tabular}{l}
+dvdisaster.com\\
+dvdisaster.de\\
+dvdisaster.net\\
+dvdisaster.org
+  \end{tabular}
+\end{center}
+
+All domains are forwarded to the same site at dvdisaster.net.
+No other internet or download sites are run by the dvdisaster project.
+
+\paragraph{No money or personal data required.}\quad
+
+\smallskip
+
+There is {\bf no registration process} for using this software.
+The dvdisaster project {\bf never} asks you to enter personal data,
+to pay a fee or to donate money for:
+
+\smallskip
+
+\begin{tabular}{ll}
+$\bullet$ & using its internet and download sites,\\
+$\bullet$ & downloading the software, and\\
+$\bullet$ & running the software. \\
+\end{tabular}
+
+\smallskip
+
+In fact, please do not offer any donations to the project. 
+We cannot accept them for various reasons.
+
+\paragraph{Cryptographic signature and checksums}\quad
+\smallskip
+
+dvdisaster releases are always published with cryptographic signatures
+and md5 checksums. See the \href{http://dvdisaster.net}{download site} for examples.
+Be very cautious if signatures and checksums are missing, invalid or not
+matching those published at the sites mentioned above.

documentation/user-manual/figures/puzzle.fig

@@ -0,0 +1,50 @@
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+	 8055 4680 8010 4905 8010 5220 8100 5490 8235 5670 8505 5850
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documentation/user-manual/local.tex

@@ -0,0 +1,7 @@
+% A link printed in parenthesis
+
+\newcommand{\plnk}[2]{\hyperref[#1]{($\hookrightarrow$ #2)}}
+
+% A text passage used as a link
+
+\newcommand{\tlnk}[2]{\hyperref[#1]{#2}}

documentation/user-manual/manual.tex

@@ -0,0 +1,138 @@
+\documentclass[12pt,a4paper,twoside]{article}
+\usepackage{times}	% Skalierbarer und lesbarer Zeichensatz
+\usepackage{ucs}	% Benötigt für Eingabe von unicode-Zeichensätzen
+\usepackage[utf8x]{inputenc} % Aktiviert Eingabe von unicode-Zeichensätzen
+\usepackage{epsfig}	% Makros zum Einfügen von Grafiken
+\usepackage{anysize}	% Makros zum Einstellen der Seitenränder
+%\usepackage{makeidx}	% Makros zum Erstellen des Indexes
+\usepackage{url}
+\usepackage{fancyhdr}
+\usepackage{listings}
+\usepackage{color}
+\usepackage[table]{xcolor}
+\usepackage{hyperref}
+
+\marginsize{30mm}{20mm}{20mm}{20mm}  % Seitenränder links, rechts, oben, unten
+\parindent0em		% Keine amerikanische Einrückung am Anfang von Paragraphen
+\renewcommand{\textfraction}{0.01}
+\renewcommand{\floatpagefraction}{0.99}
+\renewcommand{\topfraction}{0.99}
+\renewcommand{\bottomfraction}{0.99}
+
+\pagestyle{fancy}	% Seitenstil
+%\makeindex		% wird für Erstellung von Stichwortverzeichnissen benötigt
+
+\definecolor{linkblue}{rgb}{0,0,0.75}
+\definecolor{dkgreen}{rgb}{0,0.66,0}
+\definecolor{dkred}{rgb}{0.75,0,0}
+
+\definecolor{dkgrey}{RGB}{184,184,184}
+\definecolor{ltgrey}{RGB}{224,224,224}
+\definecolor{turquoise}{RGB}{128,255,255}
+\definecolor{pink}{RGB}{255,180,240}
+\definecolor{dkblue}{RGB}{196,196,240}
+
+
+\definecolor{ltgreen}{RGB}{192,255,192}
+\definecolor{ltyellow}{RGB}{255,255,192}
+\definecolor{ltorange}{RGB}{255,224,192}
+\definecolor{ltred}{RGB}{255,192,192}
+
+\hypersetup{
+    pdftitle={dvdisaster User's Manual},
+    pdfauthor={Carsten Gnörlich},
+    colorlinks=true,
+    linkcolor=linkblue,
+    citecolor=linkblue,
+    filecolor=linkblue,
+    urlcolor=linkblue
+}
+
+\input{../config/version.tex}
+\input{local.tex}
+
+% Ende der Voreinstellungen
+
+\newcommand{\paperversion}{{\em for dvdisaster version \projectversion}}
+
+\fancyhead{}
+\fancyhead[LE]{\nouppercase{\leftmark}}
+\fancyhead[RO]{\nouppercase{\rightmark}}
+%\renewcommand{\sectionmark}[1]{\markboth{#1}{#1}}
+%\renewcommand{\subsectionmark}[1]{}
+
+%\renewcommand{\footrulewidth}{0.4pt}
+\fancyfoot{}
+\fancyfoot[LE,RO]{page \thepage\ of \pageref{LastPage}}
+
+\begin{document}
+
+\definecolor{lightorange}{RGB}{255,224,150}
+\pagecolor{lightorange}
+\title{The dvdisaster User's Manual}
+\author{Carsten Gnörlich\\carsten@dvdisaster.org}
+\date{}
+\maketitle
+\thispagestyle{empty}
+
+\centerline{\includegraphics[width=40mm]{figures/puzzle.pdf}}
+
+\begin{center}
+\paperversion
+\end{center}
+
+\bigskip
+
+\begin{abstract}
+This is the {\em orange manual}, describing the usage of {\em dvdisaster}, a tool for
+creating error correction data (``ecc data'') 
+for optical media  such as CD, DVD and BD discs. 
+Use cases for creating ecc data, recovering defective media
+using ecc data and for general maintenanance of optical 
+media are given. 
+See \url{http://dvdisaster.org}  for additional resources on
+the dvdisaster project, e.g. for the {\em blue} manual (codecs.pdf)
+containing a formal specification of the error correction data format.
+\end{abstract}
+
+\vfill
+\begin{center}
+{\em 
+Copyright 2008-2015 Carsten Gnörlich.
+Verbatim copying and distribution of this entire article is permitted in any medium, 
+provided this notice is preserved.}
+\end{center}
+
+\newpage
+\nopagecolor
+
+% Table of Contents
+
+\tableofcontents
+\newpage
+
+\input{preface}
+\newpage
+
+\input{overview}
+\newpage
+
+\input{howtos}
+\newpage
+
+\input{download}
+\newpage
+
+\input{qa}
+\newpage
+
+\input{background}
+\newpage
+
+\input{burning-compatibility}
+\newpage
+
+\input{defect-reporting}
+
+\label{LastPage}\label{missing}
+\end{document}

documentation/user-manual/overview.tex

@@ -0,0 +1,256 @@
+\section{Overview}
+
+\paragraph{The challenge: Optical media eventually fail.} Optical media (CD,DVD,BD) keep their data only for a finite time (typically for many years). 
+After that time, data loss develops slowly with read errors growing from the outer 
+media region towards the inside. 
+
+\paragraph{The dvdisaster solution: Archival with data loss protection.}
+dvdisaster complements optical media \plnk{qa-technical-media}{supported media} with
+error correction data
+in a way that they are fully recoverable 
+even after some read errors have developed. 
+This enables you to rescue the complete data to a new medium.
+
+Error correction data, in short ``ecc data'',  is either added to the medium 
+or kept in separate error correction files. dvdisaster works at the image level 
+so that the recovery does not depend on the file system of the medium. 
+The maximum error correction capacity is user-selectable.
+
+\subsection{Common misunderstandings about dvdisaster}
+
+Before we describe in detail what dvdisaster can do, let's first clarify what it can't:
+
+\paragraph{dvdisaster can not make defective media readable again.}
+Like a conventional backup, error correction data must be created from 
+a fully functional optical medium - {\em you can not backup data which has already
+been lost}. When the optical medium develops defective sectors at a later time,
+those defective sectors are restored by re-calculating them from the ecc data. 
+This won't make the defective medium working again, but will produce a new iso 
+image which can be written to a new medium. 
+
+As said before, ecc data can not be created from already defective media.
+Although unreadable sectors can not be recovered in that case, dvdisaster
+might still be helpful in extracting the remaining readable portions of the medium. 
+
+\paragraph{It's not a ripping tool.} If you want a tool for copying
+protected media, you're looking at the wrong place. Such functions are
+outside the scope of dvdisaster's internal design and goals.
+Contrary to some myths saying otherwise: dvdisaster contains 
+no hidden program fragments or switches for reading protected discs.
+Check the source code for yourself if you don't trust me.
+
+ 
+\subsection{How to use this manual}
+
+Many users just want to see some examples of solving typical tasks. Flip over
+to the \tlnk{howtos}{Typical applications section} in that case. 
+
+\smallskip
+
+The remainder of this section gives an example of recovering a defective medium including
+screen shots, relates using ecc data to performing quality scans and full backups,
+and summarizes the pro and con of dvdisaster.
+
+\smallskip
+
+The \tlnk{download}{downloads} section provides a link to the download site,
+summarizes the \tlnk{download-requirements}{system requirements},
+and clarifies that you can get and use dvdisaster as
+\tlnk{download-terms}{free software, at no cost and while keeping
+your full privacy}.
+
+\smallskip
+
+There is also a chapter containing \tlnk{qa}{general questions and answers},
+\tlnk{qa-technical}{technical questions and answers}, 
+and explanations of \tlnk{qa-error}{error messages}.
+
+\smallskip
+
+The \tlnk{background}{background information} section provides details on
+the \tlnk{background-properties}{properties of the error correction},
+the difference between \tlnk{background-image-level}{image level and file level data recovery},
+the \tlnk{background-methods}{RS01, RS02 and RS03 error correction methods},
+the \tlnk{background-linear}{linear}
+and \tlnk{background-adaptive}{adaptive} reading strategies,
+some \tlnk{background-read-errors}{remarks on how media read errors come into existance},
+and finally a few \tlnk{background-eccfile-storage}{hints for storing error correction files}.
+
+\smallskip
+
+As not all optical disc burning software may be compatible with dvdisaster,
+you might want to check
+the \tlnk{burning-compatibility}{compatibility table} and the additional
+information provided with it.
+
+\smallskip
+
+If you encounter a defect (programming error) or
+incompatibility with a certain (drive) hardware and software setup,
+please see the \tlnk{reporting-defects}{reporting defects} section.
+
+%\newpage
+
+\subsection{Example of the error correction}
+
+\begin{figure}[h]
+\centerline{\includegraphics[width=\textwidth]{screenshots/recover-linear.png}}
+\caption{Reading a defective medium.}  
+\label{recover-linear}
+\end{figure}
+
+\paragraph{Recovery of aged media.} 
+The medium processed here has become discolored and partly unreadable in its outer region.
+A reading attempt yields about 23.000 unreadable sectors of 342.000 sectors total;
+resulting in about 7,2\% defective sectors. Figure \ref{recover-linear} shows the
+dvdisaster window after the reading attempt. The distribution of reading speed and
+read errors over the medium is graphically shown.
+The still readable sectors are stored in an ISO image called {\em medium.iso}.
+
+\begin{figure}[t]
+\centerline{\includegraphics[width=\textwidth]{screenshots/fix-image.png}}
+\caption{Repairing the defective image.}  
+\label{fix-image}
+\end{figure}
+
+\paragraph{Repairing the defective image.} 
+The image which has been just read is incomplete since about 23.000 sectors could
+not be read. These sectors are now reconstructed using the error correction data
+created with dvdisaster. During the recovery a maximum of 20 errors per error
+correction block is encountered (see figure \ref{fix-image}).
+This results in a peak error correction load of
+63\%, meaning that this degree of damage is handled well by error correction data
+created with default settings. The recovered image can now be written to a new medium.
+
+\paragraph{Recovery needs error correction data:}
+The recovery process described above uses error correction (``ecc'') data.
+Think of this data as a special form of backup data (it needs less space
+than a normal backup, though). Like an ordinary backup, the ecc data needs
+to be created before the medium goes defective.
+
+So if you have a defective medium but never created ecc data for it, you will
+not be able to recover the defective sectors (23.000 in the above example).
+The data located at the end of the medium will be lost, while you will probably
+be able to extract some files which are located at the beginning of the medium.
+\newpage
+
+\subsection{dvdisaster as a complement to quality scans}
+
+\tlnk{qa-quality-scans}{Quality scans}, e.g. C2 error or PI/PO scans are a valuable tool
+for testing the results of the media writing process.
+
+\smallskip
+
+But quality scans are {\bf not} a reliable means of
+{\bf predicting the lifetime} of optical media.
+Consider we are looking for the right time to copy a worn-out medium onto a new one:
+
+\begin{itemize}
+\item Too early: Copying media because of a bad quality scan is cost-ineffective.
+  Sometimes such media remain readable much longer than expected.
+\item Too late: When the quality scan reveals unreadable sectors some data has already been lost.
+\item Right before the medium fails: The ideal case, but how to tell?
+\end{itemize}
+
+However, we could do it the dvdisaster way:
+
+\begin{itemize}
+\item \tlnk{howto-ecc}{Create error correction data} for the medium.
+\item \tlnk{howto-scan}{Scan the medium} regularly. Use it until the first read errors occur.
+\item \tlnk{howto-recover}{Recover} the read errors using the error correction data.
+  Write the recovered image to a new medium.
+\end{itemize}
+
+\subsection{Error correction data vs. full backup}
+\label{overview-backup}
+
+\paragraph{A conventional backup strategy}$\!\!\!\!\!$ would be making one or 
+more copies of the optical medium. This has a few advantages:
+Copying a medium is fast, and having two (or more) working copies
+available can be convenient, especially when working at different
+locations.
+
+\smallskip
+
+The disadvantage of this approach is that it guards only against
+incidental damage, but not against general aging. It is not helpful
+to have ten copies which all decay in a similar manner. If all 
+ten copies are unreadable in the outermost region after a few years,
+data loss has occurred even though we were spending 900\% of the
+original storage capacity for the backup.
+
+\paragraph{Ecc data behaves differently}$\!\!\!\!\!$ since it is not a verbatim
+copy of the original data. It is a mathematical scheme working like
+this: Give me any 80\% of the original data and I will be able to
+reconstruct the missing 20\%, regardless of {\em where} the 20\%
+are missing (whether at the beginning or at the end, maybe in between - doesn't
+matter). Incidentally, there is a strong relationship between 
+being able to reconstruct a missing percentage of the original data 
+and the size of the ecc data: If the ecc data is 20\% of the size of
+the original data, it can roughly recover up to 20\% of missing data;
+with ecc data being 30\% of the original size up to 30\% can be recovered
+and so on. But this relationship isn't even the greatest advantage
+of the ecc data; the ``regardless of where the defects are'' is the big deal.
+
+\smallskip
+
+Let's assume we want to have a 100\% protection of a specific 4 GiByte 
+DVD. Then we create another DVD containing 4 GiBytes of ecc data. 
+At a later date, both DVDs decay and the last 30\% of both become
+unreadable. Since we have still 70\% of the original data and of the
+ecc data, everything is fine! We can still reconstruct the original 
+data from them; using the second DVD for ecc data is much more
+efficient than creating a second copy on it. In fact putting another
+copy on the second DVD would not have saved us from a 30\% data loss.
+
+\smallskip
+
+We can even make some assumptions about our media. Maybe we expect
+that even a defective medium will not lose more than 15\% of its data 
+(don't take my word on it). And we make sure that ecc data will be saved
+on a different type of medium which is considered to have a longer life than optical
+media. Then creating ecc data with a recovery rate of 20\% (always
+leave a safety margin) should suffice our needs. 
+This would yield a reasonable data protection
+while spending only an additional 20\% of storage for it. 
+
+\smallskip
+
+This is not to say that ecc data is the final answer to all
+archiving means, but when used well, it can be much more
+efficient and secure than a simple backup strategy. See also the
+\tlnk{bigpicture-backup}{``Big Picture'' section} for a continued
+ecc data vs. full backup discussion.
+
+\subsection{Pro and con of dvdisaster}
+
+To summarize from the previous sub sections:
+
+\bigskip
+{\bf Advantages of using dvdisaster:}
+
+\begin{itemize}
+\item {\bf Protects} against aging and accidental medium damage (within certain limits).
+\item \tlnk{howto-scan}{Read error tests} run {\bf faster} than quality scans; up to full reading speed depending on the drive.
+\item {\bf Cost-effective:} Media must be replaced with a new copy only when they are really defective.
+\item {\bf Space-efficient:} Ecc data requires less space than a full backup under most scenarios.
+\end{itemize}
+
+\bigskip
+{\bf Limitations of using dvdisaster:}
+
+\medskip
+
+You need a backup and testing strategy and at least 15\% of additional storage.
+
+\begin{itemize}
+\item Error correction data {\bf must be created before the medium fails}, preferably at the same time the medium is written.
+\item Error correction data requires {\bf additional storage space} either on the protected medium or by using additional media. Using the standard settings the additional storage space amounts to 15\% of the original data size (approx. 700MiB for a full 4.7GiB DVD).
+\item No guaranteed protection against data loss as limits and statistical properties of the
+  error correction may be exceeded with extremely bad luck.
+\end{itemize}
+
+\bigskip
+
+See also the \tlnk{background}{collection of background information} to learn
+more about the functioning of dvdisaster.

documentation/user-manual/preface.tex

@@ -0,0 +1,86 @@
+\section*{Preface}
+\label{preface}
+
+Since the release of dvdisaster 0.79.3\footnote{Version 0.79.4 was never finished
+and released.}, nearly five years have passed.
+This was partly due to changed circumstances in its
+primary developer's life, but there was also a lot of
+coding going on behind the scenes. In comparison with its
+predecessor, dvdisaster 0.79.5 comes with lots of its
+internals being significantly reworked.
+
+\smallskip
+
+The most visible improvement  of dvdisaster 0.79.5 is, of
+course, its multithreaded RS03 codec. While it takes
+about 62 minutes for protecting a 36 GiB image with RS02
+on a mid range PC,
+the same task is done with RS03 in less than 7 minutes
+using 6 processor cores on the same machine.
+On a high end server with at least 16 cores and very good I/O,
+this can be done in under a minute. That's quite an
+improvement.
+
+RS03 is ready for production use in the current release.
+Some non-essential features, especially reworking the
+adaptive reading for use with RS03 and multi-threaded
+RS03 decoding (media fixing) will be delivered with
+the following dvdisaster releases.
+
+\smallskip
+
+Other parts of the project had to be changed or even
+discontinued. A software project lives on development
+and continuous releases; else the
+project will eventually die. In this respect, dvdisaster
+was very endangered in the last few years.
+To prevent this from happening again, most effort
+is now directed into source code development;
+everything else is delegated or discontinued.
+Source code development basically means making
+the GNU/Linux version, which provides the code base
+for all other versions, and the FreeBSD and NetBSD ports,
+which are very easily derived from the GNU/Linux code.
+This is not the case for the Mac OS and Windows ports,
+which are, unfortunately, \tlnk{qa-discontinued-os}{discontinued} as of now.
+
+Another feature which has to go are the separate
+stable and development releases.
+Starting with this version, all dvdisaster releases
+are considered production quality, so there is no
+need for different branches anymore.
+
+\smallskip
+
+Maintaining the multi-lingual online documentation, which
+also served as the project home page, did also prove to
+be too time consuming. The project home page has
+been changed into a simple download platform for
+the project sources. It is now directed at package
+maintainers who will create and pass on binaries
+for the GNU/Linux, FreeBSD and NetBSD distributions.
+
+The program documentation, which you are reading
+right now, is provided in PDF format which is much
+easier to author than the HTML version. The only
+language available is English. Most parts of this
+manual have been adapted from the old online
+documentation, so it still feels more like a website
+than a book. While hyperlinks are not as usable in PDF
+as in HTML, they have been kept in this document to
+stress that it is intended to be used as an online reference.
+So please do our environment a favour and do not print
+this manual. It is not meant to be read
+from front cover to back cover, anyways.
+
+\smallskip
+
+Okay, enough ranting already. May dvdisaster be helpful
+in protecting and recovering your valuable data,
+and thanks for using it!
+
+\bigskip
+
+{\em -- -- cg, August 2015}
+
+

documentation/user-manual/qa.tex

@@ -0,0 +1,462 @@
+\newcounter{qasection}
+\newcounter{qaitem}
+\newcommand{\qa}[2]{\stepcounter{qaitem}{\bf Q \theqasection.\theqaitem: #1}
+
+  \medskip
+
+  #2
+
+  \bigskip}
+
+\section{Questions and answers}
+\label{qa}
+\stepcounter{qasection}
+
+This section answers some general questions on dvdisaster. There is also
+a sub section about \tlnk{qa-technical}{technical questions}, and one
+discussing \tlnk{qa-error}{error messages}.
+
+\bigskip
+
+\qa{How is ``dvdisaster'' pronounced?}
+   {Since the word stems from the english language, simply spell ``dv'' before saying ``disaster''. Perhaps ``dee-vee-disaster'' is a suitable phonetic circumscription. }
+
+
+
+\qa{What are quality scans and why don't you support more?}
+   {\label{qa-quality-scans}Optical media have a built-in error correction which is similar
+     to the method used in dvdisaster. Some drives can report the number
+     of errors corrected while reading a medium. This provides a rough
+     estimate of the writing and media qualities.
+
+     \smallskip
+     
+     Since dvdisaster is free software, it can only include code and
+     information which can be redistributed freely. This is currently
+     true for C2 \tlnk{howto-scan}{scanning} of CD media, which
+     is officially standardized
+     and has free documentation available.
+
+     \smallskip
+     
+     On the other hand, DVD quality scans (``PI/PO scans'') and BD disc
+     scans are not standardized. Those drive vendors who support it are
+     using proprietary programming interfaces. The respective specifications
+     seem not to be available for use in free software. So we must patiently
+     wait until manufacturers understand that having free software available
+     for a drive will sell more drives. }
+
+\qa{Is dvdisaster compatible with future releases?}
+   {Yes, dvdisaster files are intended for an archival time of many years.
+     When upgrading to a newer version of dvdisaster you can continue using
+     images and error correction data created from previous versions. There
+     is no need to recreate them again. }
+
+ \qa{Augmented images have the error correction data appended at the end of the medium. Isn't that a bad choice?}
+    {\label{qa-ecc-distribution}No. First a bit of terminology: If we augment 80 bytes of user data with 20 bytes
+      of error correction (ecc) data, we get an ``ecc block'' comprised of 100 bytes.
+      Now take the following into consideration about the ecc block:
+
+      \begin{enumerate}
+        \item The position of the error correction data within the ecc block does not matter.
+
+          The Reed-Solomon (RS) decoder does not differentiate between user data and error
+          correction data. In the view of the RS decoder our ecc block is a sequence of
+          100 bytes from which an arbitrary subset of 20 bytes can be recovered. It can
+          recover the first 20 bytes, the last 20 bytes, or any combination from within
+          as long as the remaining 80 bytes are still intact. From this it follows that
+          the position of the ecc data within the ecc block does not matter; whether it
+          is appended at the end of the user data or is interleaved with it has no
+          influence on the error correcting capability.
+
+        \item Properly distributing the ecc block offsets influence of bad media spots.
+
+          Optical media have a higher probability of failing in the outer area; but for
+          technical reasons this is the only place where the error correction data
+          can be stored. However this effect is offset by distributing the ecc block
+          content over the medium. Let's assume that our medium is filled 80\% with
+          user data, leaving the remaining 20\% free for error correction data.
+          Now consider the 100 byte ecc block again. We need to pick 80 bytes from
+          the user data for it and require 20 additional byte positions in the error
+          correction data area. Even under these constraints it is possible to evenly
+          distribute the 100 bytes over the medium, from the inside to the outside,
+          each having a maximum distance to its neighbors. This means that under the
+          above scenario, 80\% of each ecc block comes from the first 80\% of the medium,
+          and 20\% from the rest (the outer area). Together with point (1), this negates
+          the influence of bad spots on the medium. Symmetry implies that for each error
+          correction byte stored in the (bad) outer region there will be a user data
+          byte located in the (good) inner medium region.
+
+          \smallskip
+          
+          (If you do not already see the point, imagine putting the ecc data into the
+          inner medium region and the user data in the outer region. Consider point (1)
+          again to see that nothing changes with respect to the error correction.)
+      \end{enumerate}}
+
+ \qa{What's the difference between image based and file based data recovery?}
+    {\label{qa-image-level}Optical media are comprised of 2048 byte-wide sectors. Most of those
+      sectors are used to store file data, but some of them hold
+      so-called ``meta data'', e.g. information on directory folders.
+
+      In figure \ref{qa-metadata1} (below) there is a directory ``Pics'' holding
+      three files ``forest.jpg'', ``rock.jpg'' and ``protect.par''\footnote{No
+        offense intended against the PAR/PAR2 project. Carsten is just confident
+        that file based protection does not work on optical media :-)}.
+      Note how these files are mapped onto physical sectors (green/blue
+      squares) on the medium, and that an additional meta data sector
+      (red square) is needed for storing the ``Pics'' directory structure.
+
+\begin{figure}[h]
+\centerline{\includegraphics[width=\textwidth]{figures/metadata1.pdf}}
+\caption{Relation between file system and sectors on the medium.}  
+\label{qa-metadata1}
+\end{figure}
+
+\paragraph{Shortcoming of file based recovery on optical media.} Now let's assume
+that we are working with file based error correction. The file ``protect.par'' holds
+error correction information which can be used to recover unreadable sectors within the
+files ``forest.jpg'' and ``rock.jpg''. This will only work as long as we need to
+recover sectors which are part of a file. But if meta data sectors become unreadable,
+the file based protection will collapse. Consider figure \ref{qa-metadata2}.
+When the red directory sector becomes unreadable, not only the
+directory ``Pics'' but also all files under ``Pics'' become inaccessible.
+This is due to the logical structure of the ISO/UDF file system, as there is
+no way to tell how the green and blue sectors relate to files anymore when
+the directory is lost. So we have a complete data loss although all sectors
+comprising the files are still physically readable.
+
+\begin{figure}[h]
+\centerline{\includegraphics[width=\textwidth]{figures/metadata2.pdf}}
+\caption{Losing the metadata sector produces complete data loss.}  
+\label{qa-metadata2}
+\end{figure}
+
+Please note that moving ``protect.par'' to a separate medium does not rectify
+the problem - the directory block is still not recoverable as it is not
+protected by the error correction data in ``protect.par''.
+
+\paragraph{Advantages of image level recovery on optical media.} dvdisaster applies
+an image level approach to error recovery. The medium is read and processed as an ISO
+image. The ISO image contains a sequence of all sectors found on the medium, including
+those which are meta data for the file system. Since the dvdisaster error correction
+data protects all sectors in the ISO image, file contents as well as meta data
+sectors (e.g. directories) can be restored. See fig. \ref{qa-metadata3} for the
+different range of protection. 
+
+\begin{figure}[h]
+\centerline{\includegraphics[width=\textwidth]{figures/metadata3.pdf}}
+\caption{Image level protection}  
+\label{qa-metadata3}
+\end{figure}
+
+In addition, neither reading the damaged ISO image nor applying the error
+correction requires any information from the file system contained on the
+medium. As long as the drive is still able to recognize the medium, dvdisaster
+will be able to recover the still readable sectors from it. Therefore there are
+no ``single sectors of failure'' as in the file based approach. }
+
+\newpage
+\subsection{Technical questions}
+\label{qa-technical}
+\stepcounter{qasection}
+\setcounter{qaitem}{0}
+
+\qa{Which on-screen translations of the program are available?\label{qa-locale}}
+{The current version of dvdisaster contains screen texts in the following languages:
+
+\medskip
+  
+\begin{tabular}{lll}
+Czech &--& unmaintained and outdated\\
+English &--& complete\\
+German &--& complete\\
+Italian &--& unmaintained and outdated\\
+Portuguese &--& unmaintained and outdated\\
+Russian &--& unmaintained and outdated\\
+Swedish &--& unmaintained and outdated\\
+\end{tabular}
+
+\medskip
+  
+Translators for other languages are welcome!
+
+\bigskip
+
+dvdisaster will automatically obtain language settings from the operating system.
+If the local language is not yet supported, english text will be used. A different
+language can be selected using environment variables.
+
+\medskip
+
+Example for the bash shell and german language:
+
+\smallskip
+
+{\tt export LANG=de\_DE.utf8}
+
+\medskip
+
+Please note that we are currently not providing translations of this user manual
+and the internet site. See \tlnk{qa-translate}{topic Q 2.5} for more details. 
+}
+
+\qa{Which media types are supported?}
+{\label{qa-technical-media} dvdisaster supports (re-)writeable CD, DVD and BD media.
+  Media containing multiple sessions or copy protection can {\em not} be used.
+
+\bigskip
+  
+Usable media by type:
+
+\medskip
+
+{\bf CD-R, CD-RW}
+
+\begin{itemize}
+  \item only Data CD are supported.
+\end{itemize}
+
+\medskip
+
+{\bf DVD-R, DVD+R}
+
+\begin{itemize}
+\item No further limitations are known.
+\end{itemize}
+
+\medskip
+
+{\bf DVD-R DL, DVD+R DL (two layers)}
+
+\begin{itemize}
+\item The drive must be able to \tlnk{qa-identify}{identify (Q3.5)} the medium
+  type. Typically this is only the case for drives which
+  can also write two layered media.
+\end{itemize}
+
+\medskip
+
+{\bf DVD-RW, DVD+RW}
+
+\begin{itemize}
+\item Some drives report \tlnk{qa-rw}{wrong image sizes (Q3.4)}.
+
+  Remedy: Determine the image size from the ISO/UDF file system or the ECC data.
+\end{itemize}
+
+\medskip
+
+{\bf DVD-RAM}
+
+\begin{itemize}
+\item Usable only when written with ISO/UDF images like DVD-R/-RW;
+\item Not supported when used as removeable medium for packet writing.
+\item Similar issues with \tlnk{qa-rw}{image size recognition (Q3.4)} as noted above.
+\end{itemize}
+
+\medskip
+
+{\bf BD-R, BD-RW}
+
+\begin{itemize}
+\item No limitations are known so far, but very few results on the
+  two-layered type (the 50GiB variety) have been reported yet.
+\end{itemize}
+
+\medskip
+
+{\bf Not usable types} (image can not be extracted):
+
+\begin{itemize}
+\item BD-ROM (pressed BDs), DVD-ROM (pressed DVDs), CD-Audio and CD-Video.
+\end{itemize}}
+
+\qa{Which file systems are supported?}
+   {dvdisaster works exclusively on the image level which is accessed
+     sector-wise. That means it does not matter with which file system
+     the medium has been formatted. See also \tlnk{qa-image-level}{Q1.5}.
+
+     \smallskip
+     
+     Since dvdisaster neither knows nor uses the file system structure,
+     it can not repair logical errors at the file system level. It can not
+     recover lost or deleted files. }
+
+\qa{What happened to the Windows and Mac OS ports?}
+   {\label{qa-discontinued-os}As you may have noticed, the project has progressed very slowly in the
+     last years. The main developer is currently very short of time,
+     and some co-developers are also busy with other tasks. So the question
+     was either to stop development at all, or to continue developing using
+     as few resources as possible.
+
+     The main problem is that we have just one version of dvdisaster which
+     needs to live up to the different standards of GNU/Linux, Windows and
+     Mac OS. The path of least resistance is to continue developing dvdisaster
+     for GNU/Linux, since dvdisaster was originally started on GNU/Linux and is
+     still primarily developed on it. dvdisaster is a ``native'' GNU/Linux
+     application, meaning that it only uses tools and interfaces which come
+     bundled with GNU/Linux, such as the GNU compiler suite and the GTK+ graphical
+     user interface toolkit.
+
+     \smallskip
+     
+     Producing the Windows version requires a huge effort, as dvdisaster can not be
+     built with native Windows tools like Visual C++. It requires installing an
+     Unix-like development environment containing the GNU compiler suite (e.g. from
+     MingW) and a port of the GTK+ toolkit. These tools need to be obtained directly
+     from the upstream source (e.g. from www.gtk.org), as no responsible developer
+     would use pre-made binaries from third-party sites. That guarantees for huge
+     extra work every time the tool chain needs to be updated.
+
+     \smallskip
+     
+     When the project was started in the year 2004, the Windows 2000 port of GTK+
+     provided a sufficient compatibility layer to make a decent looking and usable
+     Windows version. Today, since Windows 8 the operating system has diverged so
+     significantly from GNU/Linux that it makes GTK+ based applications look poor
+     in terms of usage and visual appearance. Also, Windows is taking different
+     ways in dealing with 64-bitness and multithreading over several CPU cores.
+     This makes it very difficult to write an implementation of the RS03 codec
+     which works  well on both GNU/Linux and Windows. To create a version
+     which lives up to the current standards of both GNU/Linux and Windows,
+     dvdisaster would have to be written from scratch with native bindings
+     to the Windows GUI and process interfaces. The same is true for Mac OS;
+     necessitating another complete rewrite of the source code. Resources for
+     that are not available, so the project will just continue developing 
+     the GNU/Linux version.
+
+     \smallskip
+     
+     Please note that this does not make your error correction data immediately
+     worthless under Windows, as you can continue using the current 0.72.3 binary
+     for a long time. Also, ecc data created under Windows can be used to recover
+     media using GNU/Linux, even when booting Linux as a live system from a memory stick.}
+
+ \qa{How can I help providing translations?\label{qa-translate}}
+{There are several ways of providing translations to the project.
+
+  \paragraph{Translating the on-screen texts.} See \tlnk{qa-locale}{topic Q 2.1} for
+  a list of available translations. You are welcome to take over an unmaintained
+  translation or to provide one for a new language. Send an email to
+  {\em carsten@dvdisaster.org} for further instructions.
+
+  \paragraph{Translating the user manual and/or the internet site.} The project
+  is {\em currently not accepting contributions for translations of the internet
+    site and the user manual}. Coordinating a translation effort is a very time
+  consuming process which is currently exceeding our resources. 
+
+  \smallskip
+  
+  You are welcome, of course, to provide an unoffical translation of the
+  project documentation on your own webspace and at your own discretion. }
+
+\newpage
+
+\subsection{Error messages}
+\label{qa-error}
+\stepcounter{qasection}
+\setcounter{qaitem}{0}
+
+\qa{``Warning: 2 sectors missing at the end of the disc''}
+   {This warning appears with CD media written in ``TAO'' (track at once) mode.
+     Some drives report an image size which is 2 sectors too large for such media,
+     producing 2 pseudo read errors at the end of the medium which do not mean data
+     loss in this case.
+
+     \smallskip
+     
+     Since the writing mode can not be determined from the medium, dvdisaster
+     assumes a ``TAO'' CD if exactly the last two sectors are unreadable, and
+     trims the image accordingly. It is up to you to decide whether this is okay.
+     You can advise dvdisaster to treat these sectors as real read errors by using
+     the {\tt --dao} option or the preferences tab for reading/scanning.
+
+     \smallskip
+     
+     To avoid these problems, consider using the ``DAO / Disc at once''
+     (sometimes also called ``SAO / Session at once'') mode for writing single session media.}
+
+\qa{Program blocks right after invocation}
+   { Using old Linux kernel versions (kernel 2.4.x) the program
+     occasionally blocks right after the start and before any actions are
+     carried out. It can not be terminated using Ctrl-C or ``kill -9''.
+
+     \smallskip
+     
+     Eject the medium to make the program terminate. Insert the medium again
+     and wait until the drive recognizes the medium and spins down. Calling
+     dvdisaster again should work now. }
+
+\qa{What does ``CRC error, sector: n'' mean?}
+   {The respective sector could be read, but the checksum of its contents does
+     not match the value noted in the error correction file. Some possible causes are:
+
+ \begin{itemize}
+ \item The image has been mounted with write permission and was
+   therefore altered (typical evidence: CRC errors in sector 64 and in sectors 200 to 400).
+ \item The computer has some hardware problems, especially when communicating with
+   its mass storage devices.
+ \end{itemize}
+ 
+ If you suspect technical problems, try creating another version of the
+ image and error correction files and \tlnk{howto-info}{verify} them again. When errors
+ disappear or surface at a different locations, your computer may be
+ suffering from defective memory, broken drive cabling, or wrong CPU/system
+ frequency settings. }
+
+ \qa{Read errors or wrong image size with -RW/+RW/-RAM media\label{qa-rw}}
+    {Some drives report incorrect image sizes when -RW/+RW/-RAM media are used.
+    
+      Two common cases are:
+
+\smallskip
+
+\begin{tabular}{lp{134mm}}
+   {\em Problem 1)} & The drive reports the size of the largest image ever written to the medium, not that of the actual image. \\
+   {\em Symptoms:} &  After erasing a medium it is written with a file sized about 100MiB. But the image read back is several GiB long and contains the remainings of older images. \\[3mm]
+
+   {\em Problem 2)} & The drive reports the maximum possible medium capacity (typically 2295104 sectors) instead of the number of actually used sectors. \\
+   {\em Symptoms:} & When reading beyond a certain point of the medium, only read errors occur, but all files on the medium are still readable and complete. \\
+\end{tabular}
+
+\paragraph{Possible remedy:} Activate the option for determining the image size from
+the ISO/UDF file system or from the ECC (RS02/RS03) data.
+
+\medskip
+
+If the required ISO/UDF sectors are unreadable and you are using error correction
+files to recover damaged media there are two possible workarounds:
+
+\begin{itemize}
+\item Execute the ``Verify'' function with only the error correction
+  file being selected/given. Note down the correct image size from the
+  output and restrict the reading range accordingly.
+\item  Simply read in the image with the incorrect (larger) size.
+  When invoking the ``Fix'' function, answer ``OK'' when you are asked
+  whether the image should be truncated.
+\end{itemize}}
+
+ \qa{My self-written media is recognized as ``DVD-ROM'' and rejected.\label{qa-identify}}
+    {The medium book type has probably been set to ``DVD-ROM''. Typically,
+      a drive capable of writing the same media format is required for
+      processing the medium with dvdisaster.
+
+\smallskip
+      
+For example, a two-layered DVD+R with a wrong book type may only
+be accepted on a writer which can write to such media. Try another
+drive for reading images in these cases.}
+
+\qa{No drives appear under FreeBSD or NetBSD.}
+{ You need read {\em and} write permission for the respective device
+  (like /dev/pass1 on FreeBSD or /dev/rcd0d on NetBSD). 
+
+  Please see the respective hints in the {\tt INSTALL} file which is
+  included in the source code archive.}
+
+\qa{``Ecc file has been created with version 0.40.7.''}
+      {Some developer versions of dvdisaster mark their ecc files with a special bit.
+        This causes dvdisaster versions upto 0.65 to falsely display the above error
+        message. Please use the developer versions only together with dvdisaster
+        0.66 or newer versions. }