Disk speed is one of the main bottlenecks for virtualized environments. It is very important to have very fast disks and to measure performance. I came across an article titled "Measuring Disk Latency with Windows Performance Monitor (Perfmon)" the other day. This article isn't necessarily aimed at virtualization, but it is very handy knowledge to have on using built-in Windows tools to measure your disk performance in terms of latency. The article mentions some of the perfmon counters to keep an eye on are:
"Physical disk performance object -> Avg. Disk sec/Read counter" - Shows the average read latency.
"Physical disk performance object -> Avg. Disk sec/Write counter" - Shows the average write latency.
"Physical disk performance object -> Avg. Disk sec/Transfer counter" - Shows the combined averages for both read and writes.
The "_Total" instance is an average of the latencies for all physical disks in the computer.
Each other instance represents an individual Physical Disk.