I recently implemented a 3PAR SAN. After migrating 10-15 VMs onto it, I looked at the disk utilization. I was happy to see how good the thin provisioning in the 3PAR SAN’s operating system was working. Summary: Total space the Hyper-V servers “think” they have = 1600 GB Total space the Hyper-V servers “think” they have used = 596 GB Actual space the SAN has reserved for these LUNs =  403 GB So that counts as a savings of around 193GB worth of real disk space (32%). Sweet, eh?) Full details below.