From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: Disappointing RAID10 Performance Date: Wed, 21 Oct 2009 19:26:14 -0400 Message-ID: <4ADF9896.6090201@tmr.com> References: <715541.19877.qm@web38803.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: <715541.19877.qm@web38803.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: > --- On Fri, 10/16/09, Rob Becker wrote: > >> What command did you use to create your >> raid-10? >> > > / > mdadm --create /dev/md0 --level=raid1 --chunk=256 --raid-disks=2 missing /dev/sdb1 > swap > mdadm --create /dev/md1 --level=raid10 --layout=o2 --chunk=256 --raid-disks=2 missing /dev/sdb2 > /home > mdadm --create /dev/md2 --level=raid10 --layout=o2 --chunk=1024 --raid-disks=2 missing /dev/sdb3 > ... then copied files and later added the sda parts to the array. (RAID conversion on live system) > > No wonder it's slow, you want two far copies, this is more or less mirroring with only two drives. Using a large buffer size also helps, you hurt your performance by limiting readahead. You can also use the 'blockdev' command (--setra) to increase your readahead on the array. Just going to far should about double your speed, the other things may help more. > >> You might try >> running iostat in parallel to see if the read_balancer is >> properly >> balancing the reads between the two disks. >> > > Don't understand this as I'm a bit of a n00b... > > > --- On Fri, 10/16/09, Tomasz Chmielewski wrote: > >> 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. >> > > OK so it was a fallacy to think this would help with large files, unless more than one is involved. > You are misconfigured. -- Bill Davidsen Unintended results are the well-earned reward for incompetence.