imported zpool not persistent across reboot

[marco]

I'm on -CURRENT (r361307) and using base ZFS.
I imported a zpool that was created on SmartOS with some unsupported
feature flags so had to import it read-only.

 [~] zpool get all backup
NAME    PROPERTY                                       VALUE                                          SOURCE
backup  size                                           1.36T                                          -
backup  capacity                                       9%                                             -
backup  altroot                                        -                                              default
backup  health                                         ONLINE                                         -
backup  guid                                           11841096011823395086                           default
backup  version                                        -                                              default
backup  bootfs                                         -                                              default
backup  delegation                                     on                                             default
backup  autoreplace                                    off                                            default
backup  cachefile                                      -                                              default
backup  failmode                                       wait                                           default
backup  listsnapshots                                  off                                            default
backup  autoexpand                                     off                                            default
backup  dedupditto                                     0                                              default
backup  dedupratio                                     1.00x                                          -
backup  free                                           1.24T                                          -
backup  allocated                                      126G                                           -
backup  readonly                                       on                                             -
backup  comment                                        -                                              default
backup  expandsize                                     -                                              -
backup  freeing                                        0                                              default
backup  fragmentation                                  0%                                             -
backup  leaked                                         0                                              default
backup  bootsize                                       -                                              default
backup  checkpoint                                     -                                              -
backup  multihost                                      off                                            default
backup  feature at async_destroy                          enabled                                        local
backup  feature at empty_bpobj                            active                                         local
backup  feature at lz4_compress                           active                                         local
backup  feature at multi_vdev_crash_dump                  enabled                                        local
backup  feature at spacemap_histogram                     active                                         local
backup  feature at enabled_txg                            active                                         local
backup  feature at hole_birth                             active                                         local
backup  feature at extensible_dataset                     active                                         local
backup  feature at embedded_data                          active                                         local
backup  feature at bookmarks                              enabled                                        local
backup  feature at filesystem_limits                      enabled                                        local
backup  feature at large_blocks                           enabled                                        local
backup  feature at large_dnode                            enabled                                        local
backup  feature at sha512                                 enabled                                        local
backup  feature at skein                                  enabled                                        local
backup  feature at device_removal                         enabled                                        local
backup  feature at obsolete_counts                        enabled                                        local
backup  feature at zpool_checkpoint                       enabled                                        local
backup  feature at spacemap_v2                            active                                         local
backup  feature at allocation_classes                     enabled                                        local
backup  unsupported at com.datto:bookmark_v2              inactive                                       local
backup  unsupported at org.illumos:edonr                  inactive                                       local
backup  unsupported at com.datto:encryption               inactive                                       local
backup  unsupported at com.datto:resilver_defer           inactive                                       local
backup  unsupported at org.zfsonlinux:userobj_accounting  readonly                                       local
backup  unsupported at org.zfsonlinux:project_quota       readonly                                       local
backup  unsupported at com.delphix:log_spacemap           readonly                                       local

Whenever I reboot that zpool is no longer imported.

I've checked /boot/defaults/loader.conf, /etc/defaults/rc.conf but haven't seen any keys that I need to make the imported pool persistent.
I've read something on the cachefile=path setting in zpool(8) but as one can see it's set to default
I guess I must've overlooked something but haven't found it so far.

thanks

-- 
Marco van Lienen -- Unix SysAdmin
https://keybase.io/scarcry , GnuPG id: 8580E6CB
"The Tuck Pendleton machine...zero defects."