It's 6 blades, each of which have two disks in a Raid 1 configuration.
On every blade, one of the disks is marked bad - if I reseat the disk it rebuilds and is good for a short while and then one of the pair is marked bad again, though not necessarily the same one that was originally bad

The servers and disks are very new, and all disks failed at around the same time.
So the tech support guy is sending me 12 new disks to replace *all* the disks in the blades. This means I will have to swap out the currently failed drive, wait for the RAID to repair then swap out the other drive.
Sounds like a pointless exercise to me, but then as I've already been instructed to apply a firmware upgrade which isn't supported on these disks and watched as the program failed completely to do any useful update nothing surprises me.