VMware vSphere includes a number of enhancements that enable it to deliver very high I/O performance. In one study using EMC Enterprise Flash Drives (EFD) a single ESX host was able to achieve just above 350,000 I/O operations per second - enough to host the entire Wikipedia database on a single server with room to spare!

Read more here: <a href="http://blogs.vmware.com/performance/2009/05/350000-io-operations-per-second-one-vsphere-host-with-30-efds.html">http://blogs.vmware.com/performance/2009/05/350000-io-operations-per-second-one-vsphere-host-with-30-efds.html</a>