[CentOS-virt] disk i/o benchmarking inside vm
Eric Shubert
ejs at shubes.net
Sat Oct 22 22:14:01 EDT 2011
On 10/22/2011 06:00 PM, Dennis Jacobfeuerborn wrote:
> Running iostat shows no I/O activity when running the tests for /dev/vdb
> which explains the insane numbers. The question is why I get such different
> results when both devices are defined exactly the same way?
I'm not very familiar with KVM yet (got my first real lesson today), but
I notice you said:
"In the guest the drive are running using virtio with type=raw and
cache=none." Are these KVM settings, or did you use kernel parameters on
the guest machine?
Also, what about the elevator (i/o scheduler) in the guest? In a VMware
Server2 host (on Centos, so I'm not far OT) it's best to use the
elevator=noop parameter. I wouldn't expect the elevator to skew results
quite as much as you're seeing, but what do I know? ;)
--
-Eric 'shubes'
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