There are two primary performance topics to discuss with SAN virtualization systems:
As mentioned previously, one of the disadvantages of virtualization is the possibility of introducing latency into I/O operations and slowing down application performance. This certainly is a possibility. Companies purchasing SAN virtualization products should test and verify what the performance impact may be of the systems they are considering.
The issue is that the virtualization system must first read the entire incoming I/O and interpret it and then create one or more I/Os that are retransmitted to downstream storage. Obviously this is not an architecture for SAN networks that may be stretching supported ...