Liz van Dijk over at AnandTech has written the first part of a fantastically informative primer on virtualization and the hardware required to run VMs smoothly based on their own first-hand research. A must-read if your shop is eyeing VMware ESX. Here’s a snippet:

General I/O: This is the one thing VMware will admit to causing a few applications to be simply “unvirtualizable”. ESX at this point can maintain roughly 100,000 IOPS (vSphere is rumored to push this up to 350,000) and a maximum of 600 disks, which is a relatively impressive number considering a hefty Exchange installation requires something to the tune of 5000 IOPS. Counting at roughly 0.3 IOPS per user, that would account for over 16000 users, though of course this number might vary depending on the setup and user profiles. However, there are applications that simply require more IOPS, and they’ll experience quite a lot of trouble under ESX…

Catch the rest of “Optimizing for Virtualization” here.