We have 2 connections from each server to the Md3220. I must have mistyped, each server is running with 256 GB of RAM, not MB. I am running Raid 10.
It may well be that the VMs are too much for the disk array (There doesn't appear to be any issues on the host servers) - what I'm trying to find out is how I can understand the metrics available to confirm that, and to work out if buying/enabling the High Performance option would be helpful to me, for example.