From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: Re: Disappointing RAID10 Performance Date: Fri, 16 Oct 2009 20:30:27 +0200 Message-ID: <4AD8BBC3.4030600@wpkg.org> References: <364346.70897.qm@web38808.mail.mud.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <364346.70897.qm@web38808.mail.mud.yahoo.com> Sender: linux-raid-owner@vger.kernel.org To: adfas asd Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids adfas asd wrote: > I was hoping to get better performance with RAID10 than from the raw disks, but that's turned out to not be the case. Experimenting with the readahead buffer I get these bandwidths with the following command: > # time dd if={somelarge}.iso of=/dev/null bs={readahead size} > > /dev/sd? > 1024 71.3 MB/s > 2048 71.2 MB/s > 4096 77.7 MB/s > 8192 69.4 MB/s > 16384 76.6 MB/s > > /dev/md2 > 1024 67.1 > 2048 69.1 > 4096 75.7 > 8192 64.9 > 16384 69.0 > > Using RAID10offset2 on 2 WD 2TB drives, and always the same input file. > > Why would RAID10 performance be -poorer-? If you only use your RAID-10 array for a single "dd if=bigfile of=/dev/null" then yes, it does not give you much over mirroring. If you start using your drives for two "dd if=bigfile[12] of=/dev/null" at the same time, you will notice the difference. -- Tomasz Chmielewski http://wpkg.org