Virtualization and disk performance

[Imre Gergely]

With KVM guest, is that performance measured using virtio? If not, maybe
you could try that.

On 05/12/2010 09:30 AM, David Peall wrote:
> Hi
> 
> I've been using KVM for a bunch VM's on hardy and now Lucid and with
> CPU and memory performing quite well its been no problem.  I'm now
> looking at our ageing DB server and wanting to put it in a VM but the
> disk performance is dismal or am I doing it wrong?
> I'm quite comfortable if I loose 25% or even 33% through
> virtualization as the benefits are worth it.
> 
> Here are the numbers I have so far (using dbench, ubuntu lucid and
> ext4):
> 
> Bare metal using a slice for the host OS:
>        Throughput 2586.65 MB/sec  10 clients  10 procs
> max_latency=18.029 ms
>        Throughput 3631.62 MB/sec  50 clients  50 procs
> max_latency=239.773 ms
>        Throughput 3635.12 MB/sec  100 clients  100 procs
> max_latency=458.094 ms
> 
> Guest KVM machine using a block device
>        Throughput 1130.52 MB/sec  10 clients  10 procs
> max_latency=262.047 ms
>        Throughput 513.972 MB/sec  50 clients  50 procs
> max_latency=6561.761 ms
>        Throughput 465.593 MB/sec  100 clients  100 procs
> max_latency=2520.585 ms
> 
> I tried VMware just as a comparison using a vmdk file (not even a block
> device):
>        Throughput 1482.44 MB/sec  10 clients  10 procs
> max_latency=53.682 ms
>        Throughput 2049.45 MB/sec  50 clients  50 procs
> max_latency=492.187 ms
>        Throughput 2098.71 MB/sec  100 clients  100 procs
> max_latency=681.216 ms
> 
> Using LVM was worse and Qcow2 was even worse as expected.
> 
> Thats a big pill to swallow for KVM.
> 
> Any ideas what is the best way to get disk performance using KVM.
> 
> Thanks
> 

-- 
Imre Gergely
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