[linux-lvm] cmp of inactive mirrored LV fails

starlight at binnacle.cx starlight at binnacle.cx
Fri Dec 2 18:34:24 UTC 2011

After a little digging discovered and ran 'debugfs'
and used the 'testb' command to determine that the
mirror mismatch blocks are "not in use".

So that's good.

However I am rather disturbed that LVM
mirroring appears to have bugs that allow
images to become out-of-sync.

Have read that MD is the only way to go
with any kind of RAID and now I see that
is true.  If anyone can explain what
happened here in any positive light I'd
be interested in hearing about it.  For
now I see LVM mirroring as a turkey that
should be avoided.

Additional details:

* both LVs with discrepancies are "root"
file system LVs where one or the other
is selected in differing 'grub' boot
configuration lines

* both LVs have an associated mirror log

* in the past have experienced system
lockups due to a mirrored swap volume;
reported it to RH Bugzilla and was
told there are deadlock scenarios in
the kernel and that mirrored swap
volumes are not supported.  This and
today's discovery leads me to the
conclusion that LVM mirroring is
a seriously bad idea.

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