I'm just going to point out that e-bay is full of netapp ds2246 units at under $100, shipped, ready to receive 24 of your choice of 2.5" drive...If you are concerned about performance (and have free slots) go for the 8x 800
Imho, a lot of people really overbuild storage, including myself ... have you had a look with something like iotop on your current storage when the VM's are doing normal work ?