From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Soltys <soltys@ziu.info>
Subject: Re: LVM on raid10,f2 performance issues
Date: Mon, 19 Jan 2009 08:30:22 +0100
Message-ID: <49742C0E.6080402@ziu.info>
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>
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To: thomas62186218@aol.com
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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
> 
> Otherwise, your LVM will default to 256 read-ahead value, which stinks. 
> I increased my read performance by 3.5x with this one change! See below:
> 

Yea, that's the general idea, besides proper alignment. It wokred nice 
for Holger as well. Specifying (popular for some reason) 65536 is quite 
an overkill though, imho.