It might not be the SAN but the fact you have only a single controller and are saturating the the controller because SQL and Exchange are rather data intensive. What type of controller do you have?
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Are you using SCSI disks or SATA? SCSI is rather slow and running SQL & Esch makes it very very slow. I don't know what the backend controller interface is to each disk but from my experince SCSI MSA Type HP disk storage just does not have the horse power for SQL & Exch.
Have you checked to see if the controller interface is getting hammered?
The only thing I can think of is make sure your RAID set uses the best performing RAID config and use either 64KB or 128KB block sizes when you build the RAID sets. On the VM's format the data disks using 16K or 32K or 64K cluster sizes. Using the default 512 in the VM will kill your performance. Also, if you have RAM to spare use it all.