zpool unusable on all pools when one pool has a problem
When I got to a state where one zpool command on a test pool was stuck (issue #7328), I noticed that running zpool on other pools which had no underlying problems was not possible, they all became stuck in the same way (unkillable):
# zpool status rpool ^CConnection to nfsserv2 closed by remote host. Connection to nfsserv2 closed.
The only solution was to push the reset button (even software reboot was stuck).