IBM & Red Hat were able to achieve 1+ Million DB2 transactions per second, with a cost per transaction of $0.51/tpmC. Accordingly, this is 88% of bare metal performance. This was done using what is currently a tech preview I/O vitalization technology (virtio-blk-data-plane) in RHEL 6.4. More details on the test rig are in The Register article. I was honestly a little surprised to see this was performed on a mix of legacy HDD & SSD’s.
Additionally, on the bleeding edge Gluster front, there have been implementations of Gluster FS calls directly from QEMU/KVM guests to Gluster storage. This eliminates the use of FUSE as an abstraction layer, which should be quite a performance boost. It will be interesting to see if this functionality makes its way into Red Hat Storage & the RHEV product, to provide higher performance access to commodity storage exposed via Red Hat Storage. No timeline on that – though a tech preview will probably come first.
As mentioned, these are currently community efforts &/or tech previews, but I think they give a good indication of what Red Hat is working on and how (along with partners, community & customers) Red Hat is leading innovation in the space.