110 lines
7.1 KiB
Markdown
110 lines
7.1 KiB
Markdown
# :cd: What is dvdisaster?
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**dvdisaster** provides additional [ECC](https://en.m.wikipedia.org/wiki/Error_correction_code) protection for optical media.
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If a medium gets damaged, dvdisaster can recover it as long as the amount of damage is smaller than the amount of ECC data you added to protect it.
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It can loosely be compared to [.par2](https://en.m.wikipedia.org/wiki/Parchive) files, but the protection works at the *iso* level instead of working at the file level.
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This way, even if metadata from the optical medium filesystem is damaged, dvdisaster can still work flawlessly.
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Please refer to the [PDF manual](documentation/user-manual/manual.pdf) for more information.
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# :wrench: Unofficial version
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The last upstream version by Carsten Gnörlich is dated 2017, and could be found on the
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[official](https://web.archive.org/web/20180428070843/http://dvdisaster.net/en/index.html)
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[website](https://web.archive.org/web/20180509154525/http://dvdisaster.org/en/index.html)
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which is [now](http://www.dvdisaster.net) [down](http://www.dvdisaster.org).
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The original source code [repository](https://sourceforge.net/projects/dvdisaster/files/dvdisaster) doesn't have it,
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but [Debian sources](https://sources.debian.org/src/dvdisaster/) does, thanks to the maintainer there.
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The original [README](README) has been left untouched in this repository.
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This version is built on top of the latest upstream version, with the following notable enhancements:
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- Added pre-defined sizes for BD-R Triple Layer (100GB), BD-R Quadruple Layer (128GB)
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- Added an option to use more space for ECC on BD-R
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- Windows build supported again (it was dropped upstream a few versions back)
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- A new CLI-only version, not depending on gtk (`./configure --with-gui=no && make clean && make -j4`)
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- Non-regression tests on each code change, for Linux64 and Windows32/64, CLI and GUI versions
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- Prebuilt binaries for Windows32, Windows64, Linux64 (static builds and AppImage builds), CLI and GUI versions
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- Fixed a bunch of (minor) quirks, a few (minor) bugs, added a couple (minor) features
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Please refer to the [CHANGELOG](CHANGELOG) for all the details.
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In 2021, upstream development briefly resumed [on a new website](https://dvdisaster.jcea.es/).
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The new team successfully picked up some of the improvements of this unofficial version.
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If/when upstream resumes development again, their changes will be merged back here when possible.
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In any case, even if at some point we succeed in upstreaming all our patches, and both codebases are exactly the same,
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this repository will stay up as it provides automated tests and prebuilt binaries.
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This version will never break compatibility with upstream versions,
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the goal is to ensure an optical media protected by upstream dvdisaster will still be able to be repaired
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with this version 10+ years from now. Regression tests are here to ensure this is the case.
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## :twisted_rightwards_arrows: 3 available protection modes ("codecs")
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For a more detailed explanation of the algorithms, please refer to the [codecs specification PDF](documentation/codecs.pdf).
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:one: **RS01** creates error correction files which are stored separately from the image they belong to.
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The artefact is an **ecc** file, which must be stored on another media than the one we're protecting.
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:two: **RS02** creates error correction data which is added to the medium to protect, we call this *augmenting* the image we're protecting.
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Damaged sectors in the error correction information reduce the data recovering capacity,
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but do not make recovery impossible - a second medium for keeping or protecting the error correction information is not required.
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:three: **RS03** is a further development of RS01 and RS02. It can create both error correction files and
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augmented images, with the following added features:
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- RS03 can use multiple CPU cores and is therefore **much** faster than RS01/RS02 on modern hardware.
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- RS03 error correction files are - contrary to RS01, and to a lesser extent RS02 - robust against damage.
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- RS03 is 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.
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The changes for parallel computation and higher robustness make RS03 a bit less space efficient,
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e.g. RS03 error correction data has slighly less (around -3%) error correction capacity than its RS01/RS02 counterparts on images with equal size.
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Rough comparison table:
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| Codecs | RS01 | RS02 | RS03 |
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|------------------|--------------------------------|--------------------------------|--------------------------------|
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| Robustness\* | :star: | :star::star::star: | :star::star::star::star::star: |
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| Speed | :star::star: | :star: | :star::star::star::star::star: |
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| Space efficiency | :star::star::star::star::star: | :star::star::star::star::star: | :star::star::star::star: |
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| Augmented images | :x: | :heavy_check_mark: | :heavy_check_mark: |
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| Separate files | :heavy_check_mark: | :x: | :heavy_check_mark: |
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\*Robustness against corruption of the dvdisaster-added ECC parts themselves
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# :bulb: Rationale
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Even if the optical media era is sunsetting now, and has been for a few years, it's still of some value for off-site backups.
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In any case, we still have media in our hands that we want to be able to repair, should it be damaged, during the next years/decades.
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Repairing is actually pretty much the very reason of dvdisaster existence (as long as parity data has been added, of course).
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The idea of this unofficial version is to ensure dvdisaster doesn't get hard to find, use or compile, ~~should upstream development never resume (we hope it does!)~~
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This is also why precompiled Windows binaries and a precompiled static CLI-only Linux version are available here.
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# :hammer: Compiling
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See the [INSTALL](INSTALL) file. The [workflow file](.github/workflows/release.yml) that is used to automatically build binaries for each release can also help.
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# :camera: Screenshots
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### Reading a damaged CD under Windows:
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### Verifying the ECC correction data from the damaged image:
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### Repairing the damaged image thanks to augmented data:
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### Verification of the image after correction:
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### Reading a quad-layer multi-session BDXL with Linux GUI:
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Note that the disc still has some room for more sessions (capacity is 128 GB).
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