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

To: Fabian Zimmermann <xen-users@xxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] How to get rid of IO-Bottleneck?
From: Taeho Kang <tkang1@xxxxxxxxx>
Date: Fri, 3 Apr 2009 16:06:41 +0900
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If all of your guest domain VM's are running on one or two HDD's... then it's no good as VM's are trying to read/write all over the HDD's. (e.g. lots and lots of random accesses across the disk)
If you've got multiple HDD's, then have your Xen guest domains running on top of each disk. If one of your VM is very much disk I/O intensive, then you would dedicate a HDD to that VM, and have other less disk I/O intensive VM's on another HDD. Just do whatever you can to balance out loads on your physical HDD's.
Or if you could have SSD (Solid State Disks) then you wouldn't have to think about this issue as it's good for random accesses.
On Fri, Apr 3, 2009 at 3:30 PM, Fabian Zimmermann <xen-users@xxxxxxxxxxxxxxxxx> wrote:

I'm running a Xen (Debian Lenny / 3.3.1 / / 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?


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