Some things i came across when I was setting up a new Linux KVM host:

• Which scheduler on the host ist the one to go for?

I was playing around with the available schedulers but thankfully someone else did that before.

See Bugreport  #505695 on the RedHat Bugzilla.

• Which scheduler on the VM ist the on to go for?

In the "Redhat Oracle 10G best practices document" (PDF) they suggest the "noop" scheduler.

It states, that with the "noop" scheduler, the host is able to optimize the I/O request, which is what we want.

Further, the RedHat Bugreport #505695 suggest  to "put virtio-blk devices in rotational mode".

At least I couldn't find a kernel parameter to enable this at boot time (if someone knows, please let me know),

so this has to be done on every VM by hand (or add the following to a start script like /etc/conf.d/local.start):

The VMs should be started without a "drive cache". For "qemu-kvm" start the VMs with

And don't forget to enable "KSM" for page merging in Kernel 2.6.32 and later. Why? See here.