On closer examination, I see that my pool is mounted under /mnt/mnt/data-tank instead of /mnt/data-tank, and there are new docker and .ix-apps directories in /mnt. Maybe I did something when I was cleaning up the mess left by the old faulted pool that caused the new pool to be mounted in the wrong place… I can see that not being able to find its pool would cause the behavior I saw with docker.