Greetings:
 
I am new to the NetApp world and am looking for some advice/guidance. We  purchased a NetApp 3020i with two shelves (10K 144GB FC drives) a few months ago. We have now placed an order for 4 additional shelves (fully loaded) with 10K 144GB drives.
 
The current configuration is one large RAID DP Group with 1 HotSpare (27 Disk DP RAID Group), which belong to one aggregate (aggr0).
 
My question:
 
  1. The new enclosures, should I create 2 x 28 Disk DP RAID groups and add it to the existing aggregate? The application we run is IO intensive and more spindles the better. Does anyone see any disadvantages of doing the above?
  2. Does anyone have a formula to calculate mean time to Repair on the 10K 144GB disks on a busy filer? I only have one hot spare disk, should I add more, is there a rule of thumb?
  3. We currently have multiple volumes on the filer, after adding the new shelves/spindles, if I run a reallocate  on the existing volumes, would it take advantage of the additional spindles.
 
Any help/guidance greatly appreciated.
 
Thanks,
Darish.