Luca Berra wrote:
I will try to explain better,
the problem is not related to the confusion between B or B'
the problem is that on one disk we have B' _without_ C.
You're demanding full atomic commits; this is precisely what journals
and /barriers/ are for.
Are you are bypassing them in a quest for performance and paying for
it on crashes?
Or is this a hardware bug?
Or is it some glitch in the block device layering leading to barrier
requests not being honored?
I just asked for confirmation that with /barriers/ the scenario above
would not happen.
I think so, that it would not happen: the filesystem would stay
consistent. (while the mismatches could still happen)
The problem is that the barriers were introduced in all md raids in the
2.6.33 (just released), and also I have read XFS has a major performance
drop with barriers activated. People will be tempted to disable
barriers. AFAIR the performance drop was visible with 1 disk alone,
imagine now with RAID. And I expect similar performance drops with other
filesystems, correct me if I am wrong.
Now it would be interesting to understand why the mismatches don't
happen when LVM is above MD-raid!?
The mechanisms presented up to now on this ML for mismatches don't
explain why on LVM the same issue doesn't show up. I think.
So you might want to use raid-1 and raid-10 under LVM, just in case....
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