[CentOS-virt] BAD disk I/O performance

Sun May 4 12:20:26 UTC 2014
Dennis Jacobfeuerborn <dennisml at conversis.de>

On 04.05.2014 12:58, Luca Gervasi wrote:
> Hello,
> i'm trying to convert my physical web servers to a virtual guest. What i'm
> experiencing is a poor disk i/o, compared to the physical counterpart
> (having strace telling me that each write takes approximately 100 times the
> time needed on physical).
> Tested hardware is pretty good (HP Proliant 360p Gen8 with 2xSAS 15k rpm 48
> Gb Ram).
> The hypervisor part is a minimal Centos 6.5 with libvirt.
> The guest is configured using: VirtIO as disk bus, qcow2 storage format
> (thick allocation), cache mode: none (needed for for live migration - this
> could be changed if is the bottleneck), IO mode: default.
> Is someone willing to give me some adivices? :)

Have you tried using a raw images just for testing? I've seen some
pretty nasty performance degradation with qcow2 but unfortunately I was
never able to track down what exactly caused this. Switching to raw
images fixed the issue for me.