From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miquel van Smoorenburg Subject: Re: O_DIRECT to md raid 6 is slow Date: Tue, 21 Aug 2012 16:51:23 +0200 Message-ID: <5033A06B.30508@xs4all.net> References: <502B8D1F.7030706@anonymous.org.uk> <201208152307.q7FN7hMR008630@xs8.xs4all.nl> <502CD3F8.70001@hardwarefreak.com> <502D6B0A.6090508@xs4all.net> <502DF357.8090205@hardwarefreak.com> <502E2817.8040306@xs4all.net> <502F237D.6060806@hardwarefreak.com> <502F698C.9010507@msgid.tls.msk.ru> <50305AB9.5080302@hardwarefreak.com> <5030F1C6.90205@hesbynett.no> <50317804.9010701@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <50317804.9010701@hardwarefreak.com> Sender: linux-kernel-owner@vger.kernel.org To: stan@hardwarefreak.com Cc: David Brown , Michael Tokarev , Linux RAID , LKML List-Id: linux-raid.ids On 08/20/2012 01:34 AM, Stan Hoeppner wrote: > I'm glad you jumped in David. You made a critical statement of fact > below which clears some things up. If you had stated it early on, > before Miquel stole the thread and moved it to LKML proper, it would > have short circuited a lot of this discussion. Which is: I'm sorry about that, that's because of the software that I use to follow most mailinglist. I didn't notice that the discussion was cc'ed to both lkml and l-r. I should fix that. > Thus my original statement was correct, or at least half correct[1], as > it pertained to md/RAID6. Then Miquel switched the discussion to > md/RAID5 and stated I was all wet. I wasn't, and neither was Dave > Chinner. I was simply unaware of this md/RAID5 single block write RMW > shortcut Well, all I tried to say is that a small write of, say, 4K, to a raid5/raid6 array does not need to re-write the whole stripe (i.e. chunksize * nr_disks) but just 4K * nr_disks, or the RMW variant of that. Mike.