Neil Brown wrote:
On Tuesday March 6, rabbit@xxxxxxxxx wrote:
>
Though it is less likely, a regular filesystem could still (I think) genuinely write different data to difference devices in a raid1/10. So relying on mismatch_cnt for early problem detection probably isn't really workable. And I think that if a drive is returning bad data without signalling an error, then you are very much into the 'late' side of problem detection.
I agree with the later, but my concern is not that much with the cause, but with the effect. From past discussion on the list I gather that no special effort is made to determine which chunk to take as 'valid', even though more than 2 logically identical chunks might be present (raid1/10). And you also seem to think that the DMA syndrome might even apply to plain fast-changing filesystems, left alone something with multiple layers (fs on lvm on raid). So here is my question: how (theoretically) safe it is to use a raid1/10 array for something very disk intensive, e.g. a mail spool? How likely it is that the effect you described above will creep different blocks onto disks, and subsequently will return the wrong data to the kernel? Should I look into raid5/6 for this kind of activity, in case both uptime and data integrity are my number one priorities, and I am willing to sacrifice performance?
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