ZFS: I/O error - blocks larger than 16777216 are not supported

Hi all,

I've been reported ZFS boot disable problem [1], and found
that this issue occers form RAID configuration [2]. So I
rebuit with RAID5 and re-installed 12.0-CURRENT
(r333982). But failed to boot with:

ZFS: i/o error - all block copies unavailable
ZFS: can't read MOS of pool zroot
gptzfsboot: failed to mount default pool zroot

FreeBSD/x86 boot
ZFS: I/O error - blocks larger than 16777216 are not supported
ZFS: can't find dataset u
Default: zroot/<0x0>:

In this case, the reason is "blocks larger than 16777216 are
not supported" and I guess this means datasets that have
recordsize greater than 8GB is NOT supported by the
FreeBSD boot loader(zpool-features(7)). Is that true ?

My zpool featues are as follows:

# kldload zfs
# zpool import 
   pool: zroot
     id: 13407092850382881815
  state: ONLINE
 status: The pool was last accessed by another system.
 action: The pool can be imported using its name or numeric identifier and
        the '-f' flag.
   see: http://illumos.org/msg/ZFS-8000-EY
 config:

        zroot       ONLINE
          mfid0p3   ONLINE
# zpool import -fR /mnt zroot
# zpool list
NAME    SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
zroot  19.9T   129G  19.7T         -     0%     0%  1.00x  ONLINE  /mnt
# zpool get all zroot
NAME   PROPERTY                                  VALUE                                     SOURCE
zroot  size                                      19.9T                                     -
zroot  capacity                                  0%                                        -
zroot  altroot                                   /mnt                                      local
zroot  health                                    ONLINE                                    -
zroot  guid                                      13407092850382881815                      default
zroot  version                                   -                                         default
zroot  bootfs                                    zroot/ROOT/default                        local
zroot  delegation                                on                                        default
zroot  autoreplace                               off                                       default
zroot  cachefile                                 none                                      local
zroot  failmode                                  wait                                      default
zroot  listsnapshots                             off                                       default
zroot  autoexpand                                off                                       default
zroot  dedupditto                                0                                         default
zroot  dedupratio                                1.00x                                     -
zroot  free                                      19.7T                                     -
zroot  allocated                                 129G                                      -
zroot  readonly                                  off                                       -
zroot  comment                                   -                                         default
zroot  expandsize                                -                                         -
zroot  freeing                                   0                                         default
zroot  fragmentation                             0%                                        -
zroot  leaked                                    0                                         default
zroot  feature_at_async_destroy                     enabled                                   local
zroot  feature_at_empty_bpobj                       active                                    local
zroot  feature_at_lz4_compress                      active                                    local
zroot  feature_at_multi_vdev_crash_dump             enabled                                   local
zroot  feature_at_spacemap_histogram                active                                    local
zroot  feature_at_enabled_txg                       active                                    local
zroot  feature_at_hole_birth                        active                                    local
zroot  feature_at_extensible_dataset                enabled                                   local
zroot  feature_at_embedded_data                     active                                    local
zroot  feature_at_bookmarks                         enabled                                   local
zroot  feature_at_filesystem_limits                 enabled                                   local
zroot  feature_at_large_blocks                      enabled                                   local
zroot  feature_at_sha512                            enabled                                   local
zroot  feature_at_skein                             enabled                                   local
zroot  unsupported_at_com.delphix:device_removal    inactive                                  local
zroot  unsupported_at_com.delphix:obsolete_counts   inactive                                  local
zroot  unsupported_at_com.delphix:zpool_checkpoint  inactive                                  local
# 

Regards

[1] https://lists.freebsd.org/pipermail/freebsd-current/2018-March/068886.html
[2] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=151910

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KIRIYAMA Kazuhiko