Cannot export/import ZFS pool

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

NetBSD  9.1_STABLE NetBSD 9.1_STABLE (XEN3_DOMU) #0: Sat Jan  9 19:31:08 
UTC 2021 mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/xen/compile/XEN3_DOMU amd64

zfs.kmod has been built with MAXPHYS=32768 as it's a -9 DomU

# /etc/rc.d/zfs rcvar
# zfs
$zfs=YES
# zpool create tank /dev/xbd1d
# zpool list
NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
tank  99.5G    95K  99.5G         -     0%     0%  1.00x  ONLINE  -
# zpool export tank
# zpool import tank
cannot import 'tank': no such pool available

This does not seem right.

As an aside, https://wiki.netbsd.org/zfs/ says to use the character device 
for zpool create, but this does not work:

# zpool create tank /dev/rxbd1d
cannot create 'tank': invalid argument for this pool operation

zpool import -a does not work. The only way I managed to get the pool back 
was the following. zpool import -d expects a directory, not just a list of 
devices.

# mkdir zdev
# ln /dev/xbd1d zdev
# zpool import -d /root/zdev
   pool: tank
     id: 2018579119307871069
  state: ONLINE
 action: The pool can be imported using its name or numeric identifier.
 config:

tank                ONLINE
  /root/zdev/xbd1d  ONLINE
# zpool import -d /root/zdev tank
# zpool list
NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
tank  99.5G   138K  99.5G         -     0%     0%  1.00x  ONLINE  -

--
Stephen