From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ethan Wilson Subject: Re: Extremely High mismatch_cnt on RAID1 system Date: Tue, 07 Oct 2014 15:14:22 +0200 Message-ID: <5433E72E.60805@shiftmail.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 04/10/2014 15:46, Dennis Grant wrote: > 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. Recently some changes in the raid1 resync algorithm introduced some bugs that could possibly generate additional mismatches, but if you haven't had resyncs then I am not so sure if such bugs and their fixes are relevant. However the fixes are here: https://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.14.20 search for "raid". You might want to upgrade to kernel 3.14.20, which is probably not what your Ubuntu LTS has currently, then repair the arrays, then see if they grow again. Note that you need to do repair and not check: echo repair > /sys/block/md0/md/sync_action at the next "check" the mismatch_cnt should be 0 (not just after "repair", because that would count the number of mismatches that have been repaired). I'd say that mismatches in general are pretty worrisome, they shouldn't happen, they are likely to indicate corruption, so if what I said doesn't work, e.g. mismatches grow again, try to report it again on the list and somebody might be able to help further to track down this problem. Regards EW