RE: [Xen-users] How to get rid of IO-Bottleneck?

["Robert Dunkley" <Robert@xxxxxxxxx>]

I have seen lower performance with fake/software raid (Higher CPU load
and no raid 1 read interleaving) but not enough to be a serious deal
breaker for light use. 

A decent cached raid controller should help in the situation below as it
should reorder writes and reduce disk write thrashing. SSDs would pretty
much eliminate the problem but since the user has 1Tb disks I assume
SSDs will not provide enough storage for the money.

Rob

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Martin
Fernau
Sent: 03 April 2009 08:19
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] How to get rid of IO-Bottleneck?

I have the same performance issues on systems using fakeraid.
Systems with a real active raid controller using SAS harddrives haven't
this 
problem. They are running as mooth as a standalone system.
If you too using fakeraid (meaning that you use dodmraid) or software
raid 
then I'm afraid that you can't do much here. This is because the raid
system 
consumes some amount of your cpu power to calculate and maintain the
raid 
system.

Regards,
Martin

> Hi,
>
> I'm running a Xen (Debian Lenny / 3.3.1 / 2.6.18.8 / 2x1T SATA RAID1 /
> 8G RAM)-Server with ~8-12 VMs (LVM based - NOOP shedule). Each VM is
> running Postgre, Tomcat, Apache. If we do our daily testings, the
> disk-io-performance  is terrible.
>
> As far as I understood reads are cached within the VMs, so this should
> not be the problem. I think the high number of writes is killing the
> hdd. Is there a way to do something like "async write", or what else
> could I do to speedup the VMs even if there is a lot of disk-io?
>
> Thanks,
> Fabian
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users


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