These indexes contain file hashes that can be used to quickly identify the target files and verify their integrity.īecause the index files were so small, they minimized the amount of extra data that had to be downloaded from Usenet to verify that the data files were all present and undamaged, or to determine how many parity volumes were required to repair any damage or reconstruct any missing files. Parchive included the construction of small index files (*.par in version 1 and *.par2 in version 2) that do not contain any recovery data.
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If any of the data files were damaged or lost while being propagated between Usenet servers, users could download parity files and use them to reconstruct the damaged or missing files. With the introduction of Parchive, parity files could be created that were then uploaded along with the original data files. Large files were broken up to reduce the effect of a corrupted download, but the unreliable nature of Usenet remained.
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Later Usenet software allowed 8 bit Extended ASCII, which permitted new techniques like yEnc. Various techniques were devised to send files over Usenet, such as uuencoding and Base64. Another limitation, which was acceptable for conversations but not for files, was that messages were normally fairly short in length and limited to 7-bit ASCII text. Usenet was originally designed for informal conversations, and the underlying protocol, NNTP was not designed to transmit arbitrary binary data. Parchive was intended to increase the reliability of transferring files via Usenet newsgroups. An alpha version of the PAR3 specification has been published on Janu while the program itself is being developed. A new PAR3 specification has been worked on since Apby PAR2 specification author Michael Nahas. The original SourceForge Parchive project has been inactive since April 30, 2015. Despite the name, Parchive uses more advanced techniques (specifically error correction codes) than simplistic parity methods of error detection.Īs of 2014, PAR1 is obsolete, PAR2 is mature for widespread use, and PAR3 is a discontinued experimental version developed by MultiPar author Yutaka Sawada. Parchive was originally written to solve the problem of reliable file sharing on Usenet, but it can be used for protecting any kind of data from data corruption, disc rot, bit rot, and accidental or malicious damage.
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Parchive (a portmanteau of parity archive, and formally known as Parity Volume Set Specification ) is an erasure code system that produces par files for checksum verification of data integrity, with the capability to perform data recovery operations that can repair or regenerate corrupted or missing data.
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