From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Rabbitson Subject: Re: LVM on raid10,f2 performance issues Date: Mon, 19 Jan 2009 08:28:20 +0100 Message-ID: <49742B94.8090407@rabbit.us> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <8CB47EBD70FE9E8-AC4-981@WEBMAIL-DG06.sim.aol.com> Sender: linux-raid-owner@vger.kernel.org To: thomas62186218@aol.com Cc: soltys@ziu.info, mauermann@gmail.com, keld@dkuug.dk, linux-raid@vger.kernel.org List-Id: linux-raid.ids 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.