From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: RAID5 alignment issues with 4K/AF drives (WD green ones) Date: Sat, 31 Dec 2011 15:53:23 +0000 Message-ID: <4EFF2FF3.1080204@anonymous.org.uk> References: <4EFD5928.100@fnarfbargle.com> <4085BCC9-B901-4D96-B530-4D580A162D20@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4085BCC9-B901-4D96-B530-4D580A162D20@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Michele Codutti Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 30/12/2011 21:04, Michele Codutti wrote: [...] > This is one of many similar outputs from iostat -x 5 from the initial rebuilding phase: > avg-cpu: %user %nice %system %iowait %steal %idle > 0.00 0.00 13.29 0.00 0.00 86.71 > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %util > sda 6585.60 0.00 4439.20 0.00 44099.20 0.00 19.87 6.14 1.38 1.38 0.00 0.09 39.28 > sdb 6280.40 0.00 4746.60 0.00 44108.00 0.00 18.59 5.20 1.10 1.10 0.00 0.07 35.04 > sdc 0.00 9895.40 0.00 1120.80 0.00 44152.80 78.79 12.03 10.73 0.00 10.73 0.82 92.32 > I also build a RAID6 (with one drive missing): same results. Hang on, are you saying you see the 40MB/s speeds during the initial rebuilding phase? Yes, you will get those results. You are seeing degraded mode performance in the RAID5 just as you are in the RAID6 with a missing drive. When the array is fully built, which may well take a day or two, you can expect better. Check /proc/mdstat for the progress of the initial build. If you happen to know that your array is already in sync (which three brand new all-zero drives would be for RAID5), or want to test without waiting for a rebuild, you can use --assume-clean when creating the array. Cheers, John.