Re: LVM on raid10,f2 performance issues

[Michal Soltys <soltys@ziu.info>]

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.