Piergiorgio Sartor wrote:
Hi,
Now it would be interesting to understand why the mismatches don't
happen when LVM is above MD-raid!?
well, maybe LVM copies the buffer, and after it
plays it nice with MD, i.e. no changes on the fly.
LVM copies the buffer!?
I don't think so...
LVM is near-zero overhead, so I would be surprised if it copied the buffer.
Also I don't think it was needed in their case, except maybe if there is
an I/O at the boundary of a logical volume or LVM stripe, which would
certainly be a mistake at requestor side.
LVM also does not merge requests AFAIR. (visible with mdstat -x 1)
Or maybe, it is just one system that behaves
properly with LVM over MD.
hmm maybe...
But me also I have never seen mismatches and the only raid-1's I have
are above LVM. (except /boot but that's almost never modified)
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