Test_Copy2 was seeing 20MBytes/sec in a within-the-array copy, so that's 40MBytes/sec throughput, and not a fully streaming read/write either as it must flick from the read site to the write site. That's not far off IMO.

On the other hand, RAID5 is always going to suck for workloads with lots of small writes. That's not VMWare's fault, as it's just passing through the writes made by the operating systems inside the VMs, nor the controller's fault, as it's inherently how RAID5 works. If you don't mind buying a fourth disk, but you only need 2N amount of storage, then switching to RAID1+0 will probably be a win for the Exchange/SQL Server workload.

Peter