VDI Server Sizing and Scaling
: VMware white paper on the capacity of its latest software to host multiple desktops. "We looked into two different workloads for capacity planning guidelines. For a light worker workload an HP DL 385 G1 server could support 42 Windows XP virtual machines. For a heavy worker workload the same server supported 26 Windows XP virtual machines... [The] server considered to be at capacity when the client fails either due to a 10 percent increase in the canary time observed for the workload or when a client script fails due to predefined timeouts." This was at approx 70% CPU utilization.
"Hardware Configuration for Server Running Desktops: One HP ProLiant DL385 G1. Two 2.2GHz AMD Opteron dual-core processors, 16GB RAM, 2 Ultra 320 SCSI drives (2 × 146GB disks, 15,000 rpm)"
As expected, powering a VM on takes more CPU than un-suspending it. Buth there's another option: you can "power on approximately the number of desktop virtual machines you estimate the host can support, with the virtual machines configured to go into standby mode after a certain fixed interval. ESX Server 3.0 introduces new power management options [e.g.] Windows XP desktops are configured to Wake on LAN .. When any network traffic arrives for a virtual machine, it seamlessly wakes up from standby mode. .. Compared to the resume from suspended state or cold reset option, this activation scheme offers very fast activation (on the order of a few seconds).." 6:10:35 PM