Problems with i/o on pve kernels

Hi,

We use Debian 6.0.7 with Proxmox kernel:

Linux 2.6.32-17-pve #1 SMP Wed Nov 28 07:15:55 CET 2012 x86_64 GNU/Linux

Servel normaly handles 247 OpenVZ containers. But.. when someone of containers use active I/O operations - for example extract 1Gb tar.gz archive - server load average goes to ~2000 la.

Used scheduler - CFQ.

Can you please give any advice?