The chart below present results from testing our engineers did in conjuction with engineers at a longtime Diskeeper customer, Solvay Pharmaceuticals (now Abbott), last summer. The tests, done on VMware ESX 3.5 with direct attached storage (DAS), were specifically "proof of concept" that Windows Guest VMs need to be defragmented. A tool we frequently recommend called ReadFile was used to gauge speed of file access. Symantec AV was also run and timed.
You can view a larger image of above graph here as well: VMware performance gains.jpg (319.27 kb)
“My first impression of Diskeeper 2010, AWESOME! The ability to proactively prevent fragmentation BEFORE it happens is the Holy Grail of disk I/O management.” - Bruce McMillan, Solvay