+1 for multiple arrays.
I'd settle for just a second array, for my SSD storage that way my frequently used data such a time-machine, phone backups, newly "acquired" media and my "to be played" steam library would not need to spin up my spindle disks all the time relegating them to infrequently used media.
Having my largest capacity (expensive) disk spinning all the time isn't great.
This is the main feature I'm missing to move from an aging Synology NAS to Unraid.
Given Synology's horrible track record with me over the last two years i would gladly pay double the pro fee to get this feature