Le Fri, 03 Apr 2009 08:30:17 +0200,
Fabian Zimmermann <xen-users@xxxxxxxxxxxxxxxxx> a écrit :
> I'm running a Xen (Debian Lenny / 3.3.1 / 220.127.116.11 / 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?
You could start to investigate with the "top" command and "iostat". Iostat
will show you the actual disk
throughput. If you near your disk maximal throughput speed, then, you can
expect more from SATA HDs on
RAID1. Using top on each host, pay attention to the "%wa", it's the percentage
of wait, meaning the system
wait too much the storage. On a perfect system, "%wa" should stay down to 0.
First of all, I will buy another SATA disk to setup a RAID5 instead of
RAID1, this will improve (a
little bit) I/O performance or better, RAID0+1. Do you use RAID Software
between ? Maybe you could increase
database memory to decrease read I/O too. Finally, if you have some extra $,
try to get a SAS RAID Controller
card such as  and a couple of SAS HDs (I would say at least 4) to setup a
fast RAID5 storage group.
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