Re: [Xen-users] Difference performances between HVM and PV guest in hard disc reading

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Sun, May 24, 2009 at 7:25 PM,  <helicoterus-elih@xxxxxxxx> wrote:
>
> I perform some tests to get hard disc performance differences between HVM 
> domU and a paravirtualized one (both Debian Lenny).

first of all, make sure you do NOT use file:/ in domU config. At least
use tap:aio:

> I used hdparm ( option -t and -T) to test cache of disc and disc sequential 
> read.
> Syntax is:
> hdparm -t|-T /dev/hda1
>
> hdparm -t for hvm returns about 30 MB/sec, wheras hdparm -t for PV return 
> about 180 MB/sec.

This is normal. HVM by default should have MUCH lower disk throughput.
That's why HVM domUs need PV drivers for both Linux (included by
default on RHEL/Centos 5.3, not available yet for newer kernels) and
Windows (like GPLPV).

> hdparm -T for hvm returns about 1247 MB/sec, wheras hdparm -T for PV return 
> about 1183 MB/sec.

-T is cached result. Repeat this several times and you should find
similar output for both PV and HVM.

-- 
Fajar

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