rescue damaged tar file 7295

Michael Powe

I think you can forget about it. Modern compressors operate by specifying a position and length of previous data to copy as new data, using a window of from 4k to 64k or more into the old data (measured from the point of expansion). Once the data is fouled that reference is gone, and there is no way to recover.

The same applies to LZW compression, although the mechanism is different. There there is a remote chance that the compressor has detected a poor compression ratio and decided to reinitialize its tables, in which case some recovery would be possible. However that mechanism hasn't been used seriously for 20 years or so, due to patent problems.

That is one advantage of the zip format, i.e. each individual compressed file stands alone, so an error will only lose one file. With the tar format all files are basically concatenated into one, and the result may then be compressed.

To avoid this sort of foul up in the future, you would be well advised to insist on ECC memory in all your systems.

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