Sesame Workshop IT leader Noah Broadwater shares lessons learned during his open source virtualization project:

1. Know your systems: "Get a true baseline of how your systems are running," Broadwater says. "Two days out of the month a server may spike like crazy because a special application job kills it." Take as long a snapshot of server behavior as possible—at least one month's activity—he advises.

2. Build in extra time to test virtualized servers: "It takes a while to get it right," Broadwater says. You will need time to test how much I/O and memory your apps consume, to ensure that application performance doesn't slow down because you combine too may resource-hungry apps on the same physical server. Xen, like all virtualization tools, is relatively young and you'll need time to get used to it, he adds.

3. Don't create a nightmare on backup street: In one instance, Broadwater's IT team virtualized 4 servers onto one physical machine; all 4 VMs were scheduled to back up at the same time, and created a bottleneck for the backup software and the physical server, Broadwater says. "Think out your backup strategy. We just changed the timing. That first full backup could be a nightmare."

4. Don't feel pressured regarding management tools: One year into its virtualization project, Sesame Workshop has yet to buy any third-party management tools for virtualization, Broadwater notes, though he is now looking at adopting tools from Platespin (recently acquired by Novell) tools for physical to virtual server conversions. These tools could save his team manual labor and time when consolidating Windows physical servers, he believes.