root@xpc:~# zpool status -x
  pool: usb-zfs
 state: DEGRADED
status: One or more devices could not be used because the label is missing or
        invalid.  Sufficient replicas exist for the pool to continue
        functioning in a degraded state.
action: Replace the device using 'zpool replace'.
   see: http://zfsonlinux.org/msg/ZFS-8000-4J
  scan: scrub repaired 0B in 8h32m with 0 errors on Sun Oct 14 08:56:54 2018
config:

        NAME                        STATE     READ WRITE CKSUM
        usb-zfs                     DEGRADED     0     0     0
          mirror-0                  DEGRADED     0     0     0
            wwn-0x5000c500ab076db6  ONLINE       0     0     0
            1991173423066485644     UNAVAIL      0     0     0  was /dev/disk/by-id/wwn-0x50014ee658a36c74-part1