Okay, I'm slowly learning this. In regards to moving my mount of tank (from the failed Mini, inserted into the Mini XL) from /tank to /mnt/tank, I found that setting the mountpoint property moved it to the proper location, but the GU still couldn't see it. In any case, I was done with that set of disks, having copied off the data, so I shut it down (forgetting to export that volume first), removed the disks, and put the Mini XL's original disks back in.
I powered it up and (from the GUI) tried to import this unit's original tank volume (that had been exported earlier, via the GUI, by using the 'Detach Volume' button), but it failed to import and told me to look at 'zpool status'. I ran that, and it seems like it's still seeing the failed Mini's disks (there were four, as two mirrors, and a log device [which I always had to use -m to ignore on import, since I didn't bring the log device over], instead of the single two-disk mirror that is physically in the Mini XL now. Can you point me in the right direction? Here's the 'zpool status' output:
[root@fnmxl1 ~]# zpool status
pool: freenas-boot
state: ONLINE
scan: scrub repaired 0 in 0h0m with 0 errors on Mon Feb 6 03:45:23 2017
config:
NAME STATE READ WRITE CKSUM
freenas-boot ONLINE 0 0 0
gptid/4561e25b-439d-11e6-9d5d-d05099c09d82 ONLINE 0 0 0
errors: No known data errors
pool: tank
state: UNAVAIL
status: One or more devices could not be opened. There are insufficient
replicas for the pool to continue functioning.
action: Attach the missing device and online it using 'zpool online'.
see:
http://illumos.org/msg/ZFS-8000-3C
scan: none requested
config:
NAME STATE READ WRITE CKSUM
tank UNAVAIL 0 0 0
mirror-0 UNAVAIL 0 0 0
7020093230999759237 UNAVAIL 0 0 0 was /dev/gptid/f5ed9209-4368-11e4-b7a2-d050992ed09c
6797398022085867470 UNAVAIL 0 0 0 was /dev/gptid/f67f815c-4368-11e4-b7a2-d050992ed09c
mirror-1 UNAVAIL 0 0 0
12114334558594323339 UNAVAIL 0 0 0 was /dev/gptid/6aa8c345-467b-11e4-8cd0-d050992ed09c
17660870568216302219 UNAVAIL 0 0 0 was /dev/gptid/f798a8d9-4368-11e4-b7a2-d050992ed09c
logs
6775395539198347000 UNAVAIL 0 0 0 was /dev/gptid/b30a8a74-4d2c-11e5-86cd-d050997949e9
[root@fnmxl1 ~]#