@SimonF Yes, I tried several, "Active Streams", "File Activity" and "Open Files". The first two showed nothing, "Open Files" showed a large list including docker etc. which live on the cache drive anyway, disabled Docker and VM manager. Was only getting "find" popping up every 10 secs or so, disabled "Dynamix Cache Directories", "find" stopped popping up, nothing else in the list, still same issue.
@doron Removed both plugins as well as Dynamix System Stats and rebooted, same issue.
Every time a drive tries to spin down, there is a tiny read from that drive that wakes it up, it is like something is monitoring the drives and spins them up if they try to spin down.
The SATA drive is now fully provisioned and is in the same array, seems to spin down no problem (no files on it yet though)
Selected New Config and removed the array, drives would not spin down when in unassigned devices list either.
EDIT:
installed iotop + python 2.7 (needed for iotop)
Stopped docker, when spinning down drives, no IO at all in iotop, in GUI shows either 7.9 kb/s or 4.8 kb/s every time I try to spin down manually.
EDIT 2:
Started randomly working but not all drives can be spun down. 3 left that can't spin down... only thing that changed is I installed Dynamix SCSI Devices at some point in the last few hours (tested spin down immediately after installing and configuring it, didn't work at the time) . And the server has been up for a few hours without me rebooting for testing.