RE: [Xen-users] XEN - networking and performance

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Simon Hobson
> Sent: Thursday, October 06, 2011 4:51 PM
>
> Jeff Sturm wrote:
> 
> >One of the traps we've run into when virtualizing moderately I/O-heavy
> >hosts, is not sizing our disk arrays right.  Not in terms of capacity
> >(terabytes) but in spindles.  If each physical host normally has 4
> >dedicated disks, for example, virtualizing 8 of these onto a domU
> >attached to a disk array with 16 drives effectively cuts that ratio
> >from 4:1 down to 2:1.  Latency goes up, throughput goes down.
> 
> Not only that, but you also guarantee that the I/O is across different areas 
> of the disk
> (different partitions/logical volumes) and so you also virtually guarantee a 
> lot more
> seek activity.

Very true, yes.  In such an environment, sequential disk performance means very 
little.  You need good random I/O throughput and that's hard to get with 
mechanical disks, beyond a few thousand iops.  15k disks help, a larger chassis 
with more disks helps, but that's just throwing $$$ at the problem and doesn't 
really break through the iops barrier.

Anyone tried SSD with good results?  I'm sure capacity requirements can make it 
cost-prohibitive for many.

Jeff



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