Note that at the start of any virtualization project, before performing any physical to virtual migration, you should complete a thorough virtualization assessment, including a performance assessment—captured regularly over weeks, not a snapshot—and a hardware and software inventory. You must know the performance attributes of the server; the existing hardware attributes (third party attachments, host cards, etc); and the support requirements, including any and all third party application support requirements.
Vendors might sometimes want to rush you to the end state without going through the virtualization assessment and planning, arguing that the migration features of the software can "correct" any problems after migration into the virtual space. This, of course, is a mistake--why build any computing environment without a clear picture of the requirements.
This was first published in March 2007