...We fully expected to see some loss in throughput at the virtual disk server due to the inherent overhead of our topology; however, what we encountered was a measurably significant drop in I/O workload at the storage array as a sizeable number of read requests were satisfied out of SANmelody’s cache. Using 8KB random read requests, we were able to handle 50,000 I/O requests per second (IOPS)...
http://www.virtual-strategy.com/VSM-Labs/DataCore-SAN-Melody/-2.html