The lzip file format is designed for long-term data archiving, taking into account both data integrity and decoder availability:
A nice feature of the lzip format is that a corrupt byte is easier to repair the nearer it is from the beginning of the file. Therefore, with the help of lziprecover, losing an entire archive just because of a corrupt byte near the beginning is a thing of the past.
Lziprecover is able to recover or decompress files produced by any of the compressors in the lzip family; lzip, plzip, minilzip/lzlib, clzip and pdlzip.
If the cause of file corruption is damaged media, the combination GNU ddrescue + lziprecover is the best option for recovering data from multiple damaged copies.
If a file is too damaged for lziprecover to repair it, all the recoverable data in all members of the file can be extracted in one step with the '-D' option.
Lziprecover is able to efficiently extract a range of bytes from a multi-member file, because it only decompresses the members containing the desired data.
Lziprecover can print correct total file sizes and ratios even for multi-member files.
When recovering data, lziprecover takes as arguments the names of the damaged files and writes zero or more recovered files depending on the operation selected and whether the recovery succeeded or not. The damaged files themselves are never modified.
When decompressing or testing file integrity, lziprecover behaves like lzip or lunzip.
To give you an idea of its possibilities, when merging two copies, each of them with one damaged area affecting 1 percent of the copy, the probability of obtaining a correct file is about 98 percent. With three such copies the probability rises to 99.97 percent. For large files (a few MB) with small errors (one sector damaged per copy), the probability approaches 100 percent even with only two copies.
Lziprecover is not a replacement for regular backups, but a last line of defense for the case where the backups are also damaged.
The lziprecover package also includes unzcrash, a program written to test robustness to decompression of corrupted data, inspired by unzcrash.c from Julian Seward's bzip2.
Learn more about lzip in the Lzip Home Page.
An online manual for lziprecover can be found here.
An archive of the bug report mailing list is available at http://lists.gnu.org/mailman/listinfo/lzip-bug.
See also the lzip project page at Savannah.
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