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Re: Ext3 strangeness data loss



On Mon, Feb 03, 2003 at 10:53:08PM -0000, Bodrogi Viktor wrote:
> 
> Seems interesting.
> I forgot to mention (yes, sorry, it's important piece of information),
> that I have RAID 1 (mirrored disks), so HW problem is less possible.
> And I have reiserfs partition on the mirror too, without any problem.

Raid protects you against disk failures.  It does not protect you from
cable problems causing data corruption, or your RAID controller going
insane.  Unfortunately a lot of people seem to believe that just
because they have RAID, they are immune from hardware problems, and
then stop doing backups.  I usually hear from them after they've
gotten screwed, and when they ask if I can perform miracles....

In any case, the scenario I described (a controller/cable problem, or
an incorrectly configured IDE DMA settings) are all still possible
with RAID; RAID does not help you prevent these sorts of problems.

As far as your not noticing the problem with reiserfs that could be
because you've been lucky, and not noticed because the block addresses
causing the problem do not (yet) contain data.  But the symptoms
you've described sound very much like hardware induced errors.

> Anyway, do you have an idea how to test for HW errors?

Well, if you have a scratch partition that's not being used, you can
try using the badblocks program.  Try using the -w option, which will
do a read/write test.  This doesn't do a random access test, so it
might not detect any problems, though.

I'd suggest checking your internal cabling, and replacing the
controller cable if it looks dubious.  Making everything is well
plugged in, too.

Good luck!

						- Ted





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