There was discussion about it here some times ago, and I think the result
was that the IDE bus is reset prior to capacitors discharge and total loss
of power and disk has enough time to finish a sector --- but if you have
crap power supply (doesn't signal power loss), crap motherboard (doesn't
reset bus) or crap disk (doesn't respond to reset), it can fail.
Hmm, maybe. But I think I saw couple of such bad sectors that were only bad
because of power loss in the wild.
BTW. reiserfs and xfs depend on this feature too. ext3 is the only one that
doesn't.
Well, at least for XFS everybody tell that it should be used with UPS only if
you really care about your data. I think it has something to do with heavy
in-RAM caching this filesystem does.
System is allowed to cache anything unless sync/fsync is called. Someone
told that XFS has some bugs that if crashed incorrectly, it can lose
already synced data ... don't know. Plus it has that infamous feature (not
a bug) that it commits size-increase but not data and you see zero-filed
files.
Anyway, it looks strange to list something very fragile and potentially not
existing in the requirements... :-)
Better to list it than quitly depend on it like ext2/fat/reiser/xfs/
(maybe jfs?) do.
Could you explain where exactly do you depend on this requirement? And what
could happen if it is not true?
If you write a file in a directory and the sector is unwritable upon write
& crash, you lose those few files near it. Just the similar way you would
lose 4 files in inode table on ext2 in this case.
Thanks,
Grzegorz Kulewski
PS. Do you have any benchmarks of your filesystem? Did you do any longer
automated tests to prove it is not going to loose data to easily?
I have, I may find them and post them. (but the university wants me to
post them to some conference, so I should keep them secret :-/)
Mikulas
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