From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: LVM on raid10,f2 performance issues Date: Mon, 26 Jan 2009 14:06:03 -0500 Message-ID: <497E099B.5060805@tmr.com> References: <49332920.5010503@gmail.com> <20081201164244.GB23899@rap.rap.dk> <4935C4B3.2060404@gmail.com> <493654C7.2090909@ziu.info> <8CB47EBD70FE9E8-AC4-981@WEBMAIL-DG06.sim.aol.com> <49742B94.8090407@rabbit.us> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49742B94.8090407@rabbit.us> Sender: linux-raid-owner@vger.kernel.org To: Peter Rabbitson Cc: thomas62186218@aol.com, soltys@ziu.info, mauermann@gmail.com, keld@dkuug.dk, linux-raid@vger.kernel.org List-Id: linux-raid.ids Peter Rabbitson wrote: > thomas62186218@aol.com wrote: > >> Hi everyone, >> >> I too was seeing miserable read-performance with LVM2 volumes on top of >> md RAID 10's on my Ubuntu 8.04 64-bit machine. My RAID 10 has 12 x 300GB >> 15K SAS drives on a 4-port LSI PCIe SAS controller. >> >> I use: >> blockdev --setra 65536 /dev/md0 >> >> And this dramatically increased my RAID 10 read performance. >> >> You MUST do the same for your LVM2 volumes for them to see a comparable >> performance boost. >> >> blockdev --setra 65536 /dev/mapper/raid10-testvol >> >> > > This is incorrect. Only the readahead setting of the _last_ block device > matters. So in case you have a raid6 of 10 drives, with LUKS on top, > with LVM on top - only the readahead settings of the individual LVs > matter, nothing further down the chain is consulted. I have some old numbers which indicate that with ext3 the use of "stride=" can improve performance, although I was measuring write and just got the read numbers without really caring about them. -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark