18 May
2005
18 May
'05
11:30 a.m.
Jules Richardson wrote:
As long as we're talking about fault-tolerant archives, neither TAR nor ZIP are
acceptable. For years I've used RAR (WinRAR for windows, RAR and RAR32 for
DOS) which has "recovery record" support (parity info). A "recovery
record"
usually burns about 1% additional space (configurable up to 10%) but can
completely recover mangled compressed data if the errors are small enough (ie
no more than 512 bytes at a time, at a certain minimum distance from the next
error, etc.). For larger archives, RAR supports parity *files*, so if you
split a large archive into, say, 10 parts and 3 recovery files, you can lose up
to any 3 of all 13 files and still be able to recover everything. I do this
when archiving data to DVD-R and it has saved my butt once (BOTH DVD sets got
bitrot because of a flood).
ZIP was never built to be fault tolerant, and trying to recover a mangled TAR
file goes completely pants if the TAR has other TARs inside it.
There *are* tools that generate parity information for archive files that don't
have it themselves... The generated files look like *.PAR. Unfortunately I
don't recall the names of them, but a quick google should find them.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
The problem I
see with zip is the single table of contents at the end.
Did you try corrupting THAT with a hex editor?
Ahh, no not at the time. I've just tried it now though and it seems
remarkably good at recovering from corruption in the TOC area. Actually,
looking at the zip file it appears to have something resembling a file
header before each file in the archive as well as the TOC at the end.