From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Falgout Subject: Re: mismatch_cnt and Raid6 Date: Thu, 21 Apr 2011 08:20:16 -0500 Message-ID: <4DB02F10.8020905@gmail.com> References: <4DB02A77.8000902@gmail.com> <20110421231419.1caa2f1c@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20110421231419.1caa2f1c@notabene.brown> Sender: linux-raid-owner@vger.kernel.org Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids It takes about 23 hours per check if I don't do anything to the array, so it will be a while before I can get back to you with results. But thanks for the quick response. ./Andrew On 4/21/2011 8:14 AM, NeilBrown wrote: > On Thu, 21 Apr 2011 08:00:39 -0500 Andrew Falgout > wrote: > >> I got an error last week from a new raid6 array about a mismatch_cnt. I >> did some reading online, performed a repair action on the array, >> performed a check action, and checked for the mismatch_cnt again. The >> number was greatly reduced, but it was still there. According to mdadm, >> everything appears to be working fine. All the drives are passing short >> tests on smartctl. >> >> What is mismatch_cnt really? Should I even be concerned about this? > Yes, you should be concerned. > mismatch_cnt is a count of sectors where the parity blocks don't match the > data blocks. > > The code doesn't check every sector individually. For raid5/6 it checks 4K > at a time, so divide by 8, and that many 4K blocks are in doubt. > > So something if going wrong somewhere. > > I would run 'check' a few time and see if the number changes. > If it goes down at all, then it looks like you occasionally get bad reads > from a device. > If it only ever increases, then you are presumably getting bad writes > sometimes. > > You could: > - stop the array > - run sha1sum on each member disk, several times. > - if any one disk has an unstable result - check cabling, or replace the disk > - if more than one disk has an unstable result, replace the controller maybe. > - if all results are stable it must be a write-only problem - much harder > to work with. > > NeilBrown > > > >> The array is giving me 25-30MB/sec performance on an sshfs mount over >> the network. With a local copy I can see speeds of 50 to 60MB/sec. >> >> Thanks, >> Andrew Falgout