I don't see a way to move the root drives, all of the user data could be moved to the faster drives, but the current drives would need to stay as root. 
We've had a change of customer performance requirements on our VNX5600 that means we want to move away from our current (RAID 1/0 NL-SAS) File Storage Pool to a new one (RAID 1/0 SAS) and release the old disks. I believe that the Data Mover LUNs (~filestorage HLID 0-4) are on our NL-SAS pool, and so they will need moving, but there's no obvious way to do that. My procedure is currently looking like: How do I do step 6 and are there other things do I need to do to clear the old pool out? Thanks for any guidance!
Migrate all VNX File storage to a new set of disks and reclaim the old ones