I have recently purchased and set up a 923+ primarily due to your tutorials. It has 3-8tb ironwolf drives (again…your tutorial), I am grossly over capacity in space but the drives were on sale. Anyway, in backing up my NAS I would like to be able to use another 8tb Sata to load in to the open bay for the backup, then remove it and install another for a rotating backup keeping one off site. Thereby rotating the drives through the open (4th) bay (rather than do it with a USB connection). Logically it seems as if I should be able to do that though I can’t find that option discussed. Is it possible?
Short answer: no. You should use a USB drive for that.
Long answer: any drive in a drive bay, even if configured as a pool and volume on its own and not combined with any other drive, is part of the operating system (DSM) configuration. It is considered a fixed drive.
USB drives, on the other hand, are considered dynamic and removable.
Thank you for taking the time to respond. That is very helpful.
Oh damn, good info. I wanted to do the same as @Rickperry … so I’ve opened a new thread extending this question to TrueNAS Scale and unRAID.