103 lines
4.4 KiB
HTML
103 lines
4.4 KiB
HTML
<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<link rel="stylesheet" href="style.css">
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<title>Known problem</title>
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</head>
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<body>
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<font size=5>Known problem</font>
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<hr>
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<h3>Error of PAR clients</h3>
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<p> 
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If an error is occured in a PAR client while create/verify/repair,
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that is shown as "Error : something..." on GUI.
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When PAR client is stopped by an error,
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the output of PAR client is save in log file without option setting.
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A user may refer the log to see what is the problem.
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When a user want to report the problem by sending mail to a developer,
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he should attach the log file with the mail.
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</p>
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<p> 
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When "malloc" error happened, decrease the number of source blocks.
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If source files exist on un-writable media like CD/DVD,
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copy those files on HDD at first, then repair the copied files.
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If the source files are very large, be careful about available space of HDD.
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If you cannot open or repair files, other applications or system may prevent your file access.
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You should close others and confirm your privilege.
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</p>
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<h3>Error: checksum mismatch</h3>
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<p> 
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When "checksum mismatch" error happened, it was caused by a hardware problem (such like failure in CPU, RAM, HDD).
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Because MultiPar consumes most machine power, PC may become un-stable by high stress or over-heat.
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If MultiPar detects calculation error, it stops to avoid invalid creation or failed repair.
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Your PC should be enough stable for heavy task.
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</p>
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<p> 
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There are some solutions to try;<br>
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(1) Change BIOS setting for safe running.<br> 
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If you set over-clocking, return to the original value.
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If you set faster memory access mode, change to slower speed.<br>
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(2) Check memory error.<br> 
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Recent Windows OS has memory test feature.
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If it finds error, you must replace the bad module.
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Even when you never see a problem at daily small memory usage,
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MultiPar may use larger memory space and can reveal failure.<br>
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(3) Change MultiPar setting to disable GPU acceleration.<br> 
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There is "Hardware environment" section on "System settings" tab of MultiPar Options.
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Un-check "Enable GPU acceleration".<br>
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(4) Change MultiPar setting to disable extra feature of CPU.<br> 
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There are some check-boxes in "Extra feature".
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Un-check them one by one and test until no error.
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The order of un-checking is from "AVX2", "JIT(SSE2)", "CLMUL", to "SSSE3".<br>
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(5) Change MultiPar setting to use less number of threads.<br> 
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Move "CPU usage" slider from right to left.<br>
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(6) Change MultiPar setting to use less memory.<br> 
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Select smaller number at "Memory usage upto around".
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</p>
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<h3>Collision of Hash values</h3>
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<p> 
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If hash value of a damaged file happens to be same as hash value of its original file,
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PAR clients cannot detect the damage.
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This is very rare case, but serious problem if happen.
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Because data in complete files are used to recover damaged files,
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miss-detection of damage causes failure of recovery.
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If you get this problem, you may check files with another hash like SHA-1.
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</p>
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<p> 
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Because PAR uses MD5 hash, accidental collision problem will not happen normally.
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In addition to MD5, PAR 2.0 uses CRC-32 to check completeness,
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then the chance of miss-detection is very low.
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Caution, MD5 was broken already as cryptgraphic hash.
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When a malicious cracker modified files by forging same hash values,
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PAR clients cannot detect the intended modification.
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</p>
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<h3>Problem of PAR 1.0 specifications</h3>
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<p> 
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PAR 1.0 uses MD5 hash to distinguish source files.
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When there are files of same contents, their MD5 becomes same also.
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In this case, those files are distinguished by filename only.
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If one of them are lost and another is misnamed,
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it is difficult to determine which file is lost or misnamed.
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When a file is thought as lost, it requires parity volume to recover.
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If you know those files have same contents,
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it is much faster to copy from another file.
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</p>
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<h3>Fault of PAR 1.0 & 2.0 specifications</h3>
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<p> 
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There is a fault in the method of creating generator matrix in PAR 1.0 and 2.0.
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Rarely the matrix is not invertible, and repair will be failed.
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If you cannot repair files with enough recovery blocks,
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you would better try with different recovery blocks.
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When there are extra blocks in the set of PAR2 files,
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MultiPar tries to solve this problem automatically.
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</p>
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</body>
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</html>
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