The new hard drives were delivered today. I put them in the server and, although this is something for which the server can remain on, it went down anyway. Reason being my 2 year old who saw a shiny power button and just had to push it. I still haven't figured out how I can configure ESXi to ignore the power button. So... apologies for the unscheduled down time

The new drives have been put in a raid-5 array and it's currently initializing. We're growing from 600 to 900GB (4x300 - 300) and when that's done I'll start moving virtual machines back to this array. After that server performance should be back to normal.