[Beowulf] LVM performance problems

[Bernd Schubert]

On Friday 04 May 2007 15:40:37 Judd Tracy wrote:
> I am trying to bring up a small file server and am noticing some serious
> performance issues when using LVM.  I created a software raid /dev/md0
> which I can read at ~195MB/s using the raw raid device, but as soon as I
> put LVM on top of it the read speeds drop to ~95MB/s using a raw lvm
> partition without a filesystem.  When I use and xfs filesystem on top of
> the lvm partition it drops down to ~40MB/s.  This seems like a
> processing power issue, but the machine is a dual processor opteron
> system with 4GB of ram in it.  Does anyone have some insight into why I
> might be having such problems with the system.


try something like this: 
blockdev --setra 8192 /dev/{volumegroup}/{logical_volume}

You should also try smaller and larger numbers.

Hope it helps,
Bernd