Hello, Regarding KVM - in particular RHEL 6.1 x86_64: I just did a set of benchmarks comparing the effect of <driver name='qemu' type='raw' cache='none' io='native'/> versus <driver name='qemu' type='raw' cache='none'/> Using Oracle's "orion" tool with an XIV backend, I got: With io='native': Maximum Large MBPS=964.41 Maximum Small IOPS=11797 Minimum Small Latency=7.57 WithOUT io='native': Maximum Large MBPS=727.42 Maximum Small IOPS=7793 Minimum Small Latency=7.56 In other words, setting the io-attribute to 'native' yields a significant performance improvement. I wonder why KVM doesn't simply default to using io='native'. If that can't happen, then I wonder why libvirt doesn't set io='native' for storage attached to a guest after creation. (virt-manager sets io='native' for the first storage, attached during guest setup, but seems to forget for subsequent block-device additions). -- Regards, Troels Arvin <troels(a)arvin.dk&gt; http://troels.arvin.dk/