I have performance problems on a virtual hard drive on a VMWare ESX 4.0 virtual machine. See the weird following sequential read speed graph:
I passed the test several times, and the shape is consistent. The guest OS is Windows Server 2003 Standard Edition x86, and the virtual hard drive is formatted in NTFS.
For the record, this virtual machine worked just right on another ESX server, and has been moved to a new one, using the Migrate command.