Please help me understand the auto tiering feature. I have a couple PS6000's with 7.2k drives and one PS6100 with 15k drives. This is mixed with RDM and VMFS volumes. Today the higher spinning array is in a separate pool. 

Should they be in the same pool for auto tiering or separate pools? Does it move whole volumes or just the blocks requiring more iops in the tier? 

Thanks!