If you only have 300GB drives in production to be protected by hot spares, you should be using 300GB drives. Why use 600’s ? The only reason I can think of is that a new 600 might be cheaper than a 300. Both will do the job and I don’t even see a reason why a 600 should be slower. 1 Per 30 is ok, but consider this: how many drives have you EVER encountered that were broken in the SAME array AT THE SAME TIME ? I’ve had 2 drives at the same time just recently and I’m doing storage now since 2004.  For DMX (years ago) EMC said (I think) 3 HSs for the first 100 and 1 more for every hundred extra drives. Clariion drives don’t break any sooner than DMX drives.
Is it a good idea to have 600GB Hotspares for 300GB disks? I know the rebuild time will be greater but generally I am just curious if many have done this and should I create more than 1 HS per 30 disks if I am going to use 600GB HS for 300's
Hotspares