Re: [patch] ext2/3: document conditions when reliable operation is possible

From: Greg Freemyer
Date: Mon Aug 24 2009 - 17:12:04 EST

> The papers show failures in "once a year" range. I have "twice a
> minute" failure scenario with flashdisks.
> Not sure how often "degraded raid5 breaks ext3 atomicity" would bite,
> but I bet it would be on "once a day" scale.

I agree it should be documented, but the ext3 atomicity issue is only
an issue on unexpected shutdown while the array is degraded. I surely
hope most people running raid5 are not seeing that level of unexpected
shutdown, let along in a degraded array,

If they are, the atomicity issue pretty strongly says they should not
be using raid5 in that environment. At least not for any filesystem I
know. Having writes to LBA n corrupt LBA n+128 as an example is
pretty hard to design around from a fs perspective.

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