[CentOS-virt] BAD disk I/O performance

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? :)

Thanks

Luca