Debian 6.0 (squeeze) with qemu-kvm and libvirt from squeeze-backports
ii qemu-kvm 1.0+dfsg-8~bpo60+1
ii libvirt-bin 0.9.8-2~bpo60+2
Has 3TB sata drives with software raid and lvm. It has a sequential write speed of ~140MB/s measured with
dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync
Elevator set to cfq
Debian 6.0 (squeeze)
Uses LVM as storage. Drivers are virtio and cache='none'
Sequential write speed is considerably slower with only 25-50MB/s
Elevator set to noop
I'm kind of running out of ideas for further tweaks but I'm sure that I/O speed should be much faster because many people are reporting almost native performance with lvm.