Hello!
I’m getting ready to destroy the temporary pool that I set up when I first installed TrueNAS so that I could evacuate the data off my existing NAS. The temporary pool has a single mirror vdev.
When I installed TrueNAS SCALE, this was the only pool and vdev in the entire system, so the TrueNAS System dataset lives there.
Obviously, I need to move that before I destroy the pool. 
So, I have two choices:
- Boot Mirror: 2xNVME, with a capacity of about 426 GiB; or
- Tank (Storage Pool): multi-mirror vdev HDD pool, with capacity in excess of 45 TB.
It seems like the best option should be the NVME pool, but two concerns there:
- TrueNAS didn’t put the system dataset on the boot pool. I can’t decide if that’s because it’s smarter than me and knows something I don’t, or because it’s not smart enough and is assuming the boot pool is somehow less safe. (Maybe it assumes it’s not a mirror?) My guess (if I have to guess why this is the better option): If it’s on the main datastore pool, it’ll make restoring the entire system configuration as-is much easier if I have to move the disks where the main data store pool lives to a completely new server with a completely new boot pool. Something something import pool and go.
- I’m not sure how much space the system dataset needs vs. what the boot pool needs. Right now, the system dataset is about 1.3GiB, and I have ~426 GiB available on the boot mirror (it’s a pair of 480 GiB m.2 NVME). I can’t imagine running out of space on a system where I’m not planning to use the boot pool for anything but TrueNAS itself, but my inexperience makes me wary.
Thanks for any advice.