This article assumes a KVM guest that runs from raw or qcow2 devices using emulated ide access. Since some time now, full virtualisation for block devices is available, facilitating the benefit of paravirtualisation. Benchmarked in bonnie++, the difference looks like this, revealing a way better performance of virtio:
Sammlung von open source perfomance/stress tools
I think we’ve got a nice representative sampling overall, we’ve got Sandisk, Verbatim, PQI, Kingston, OCZ, Patriot, Ridata, Imation, HP, Adata,Corsair, Memorex, Super Talent, PNY and Transcend in this little roundup.