Generally speaking disks spin up / down fine for me in RC2, but there is one usecase where I have noticed unnecessary spin ups.
Steps to reproduce:
1. create a share which is set to "cache only"
2. wait for unraid to spin down all disks
3. access that "cache only" share (in my case from a Windows 10 PC where it is mapped as a network drive)
4. copy a file to that "cache only" share (while all other array disks are spun down!)
Expected behaviour: file gets copied to the cache drive, all array disks stay spun down
Result: (some) disks spin up, log shows "read smart" entries for those array disks
Jan 6 05:53:07 NAS emhttpd: read SMART /dev/sde Jan 6 05:53:26 NAS emhttpd: read SMART /dev/sdd