On Mon, Aug 15, 2011 at 6:05 PM, Orion Poplawski <[log in to unmask]> wrote:
> I have a server that I recently migrated from CentOS 5.6 to SL6.1.  The host
> install serves as a basic disk server and runs our nightly backups with
> amanda.  We also have several virtual machines running on it, so of which
> are mostly idle and others which can be quite busy.  Since making the move
> I'm seeing the disk and network response/performance go to hell if I have
> any non-idle VMs running.  One barometer - I have a raid10 rebuild running
> at the moment.  With no VMs I can reach 200,000K/sec resync speed.  I'm
> getting 131,000K with two idle VMs and some other basic activity.  If I
> start a busy vm, it drops to a few hundred K/sec and all disk access is very
> slow. Response to keystrokes in a network shell can be very slow as well.
>
> As anyone else experienced problems like this?  I'm not seeing any error
> messages on the host or VMs.

Have you rebuilt the virtual images? And does the underlying RAID, and
the disks, have 4096 byte blocks? If so, you will need to be quite
cautious in partitioning your disk images, because no installer in the
world can tell from scratch, inside a virtualized host, what the block
size is on the underlying hardware, and this can *kill* your
performance if it's mis-set.