Hello Al and thanks, my drives appear to be sitting in a caddy so adding new ones should be a case of just sliding them in, I also have ACU installed, in dummies terms ( I.e me ) can I just physically add two more drives and reboot, then run ACU to configure them ?, I have been on HP's site but I glaze over after a few minutes reading as I don't have the knowledge to digest it ( which is why I like sites like this one ), from what I've read it seems that RAID dumbs down to the smallest and slowest drive in the set, so as long as I add two identical drives ( capacity and speed ) I should be OK ?