@pete I would recommend that you take a look at either Overland storage a NAS SnapScale DX2 appliance that can provide a mixture of SATA and SAS drives that will work with your current virtualised setup. There is also the option, bearing in mind that you would like a mixture of SSD, SAS and SATA drives, of looking at NetApp. Of course it depends on what kind of budget you have. Are you backing up to disk/tape, any replication required and what DR you have at the present time?