On Tue, 2014-10-07 at 15:14 +0200, Ethan Wilson wrote:

On 04/10/2014 15:46, Dennis Grant wrote:

quoted

Hello all.

...

Even after multiple checks, repairs, and rebuilds, the arrays on the
bigger drives (/ and /home) are showing insanely high mismatch_cnt
values. This has me concerned.

Dennis,
since nobody more knowledgeable replied, I will try.

Some mismatches on raid1 have been there since always, and nobody ever 
deeply investigated what they were caused by, nor if they happen on 
unallocated filesystem space or on real live data. It seems that if LVM 
is between raid1 and the filesystem then they don't happen anymore, but 
again nobody is really sure of why.

Would mismatches happen if an "assume clean" was used, either for a good
reason (say to forced a dropped disk back in) or in error, so that while
the data on the secondary disk(s) becomes self correcting as new
writes/updates are performed, to all disks, should the "primary" drive
fail the second one would contain out of sync data, where it had never
been (re)written. Although which is "primary" and which is "secondary"
is I guess not really a good description.

I would have thought that doing a DD to a _FILE_ that fills up the file
system would also reduce the mismatch count, as it would force
"correct(ing)" data to all the disks, baring reserved file system
blocks/areas.
 
NOTE DD to a FILE on the file system, NOT the raid device, the latter
will DESTROY ALL data!