Re: [Xen-users] Measure disk activity in full-virtualization.

["Todd Deshane" <deshantm@xxxxxxxxx>]

On Mon, Jul 21, 2008 at 5:21 AM, Alain Barthe <ab266061@xxxxxxxxx> wrote:

2008/7/20 Todd Deshane <deshantm@xxxxxxxxx>:

Are you familiar with the work at Clarkson University regarding performance isolation?

http://clarkson.edu/~jnm/publications/isolation_ExpCS_FINALSUBMISSION.pdf

I am very surprised by this publication whose conclusion is that a full virtualised environment (VMWare) provides a perfect isolation between VMs while a para virtualised one (Xen) is good but not perfect.

Our experience concerns WMWare server and Xen, we done some subjective and practical tests (measuring the time some real huge tasks take to acheive) and listen to users complains, and the results were quite clear : on VMWare server, when a VM is very busy, its process eats all the CPU it runs on, and other VMs slow down significantly along with the host itself. When the number of VCPU exceeds the number of CPU (it is the general case), you may have a delay of several second to see the echo of the character you typed on a VM that does nothing because another one on the same host is 100% busy.

When you say VMWare Server, are you referring to ESX?

We used VMWare workstation in that paper, ESX is a different animal altogether.
 

With Xen, no such a behaviour, isolation looks like much better. That why we migrated all our servers from VMWare to Xen.

Perhaps benchmarks don't always reflect the real world...

The workload matters a lot. The version of the software and hardware configurations can matter a lot too.

Cheers,
Todd
 

--
Todd Deshane
http://todddeshane.net
check out our book: http://runningxen.com

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