これ、bug かな・・・

bug だよね・・・

$ zpool upgrade -v                 
This system is currently running ZFS pool version 14.

The following versions are supported:

VER  説明
---  --------------------------------------------------------
 1   初期バージョンの ZFS
 2   Ditto ブロック(複製されたメタデータ)
 3   ホットスペアおよびダブルパリティー RAID-Z
 4   zpool history
 5   Compression using the gzip algorithm
 6   bootfs pool property
 7   Separate intent log devices
 8   Delegated administration
 9   refquota and refreservation properties
 10  Cache devices
 11  Improved scrub performance
 12  Snapshot properties
 13  snapused property
 14  passthrough-x aclinherit support
For more information on a particular version, including supported releases, see:

http://www.opensolaris.org/os/community/zfs/version/N

'N' はバージョン番号です。

macbook(i86pc):/export/home/kazus
$ zpool get all rpool              
NAME   PROPERTY       VALUE               SOURCE
rpool  size           87.5G               -
rpool  used           25.9G               -
rpool  available      61.6G               -
rpool  capacity       29%                 -
rpool  altroot        -                   default
rpool  health         ONLINE              -
rpool  guid           10266562362930946106  -
rpool  version        13                  local
rpool  bootfs         rpool/ROOT/snv_104  local
rpool  delegation     on                  default
rpool  autoreplace    off                 default
rpool  cachefile      -                   default
rpool  failmode       continue            local
rpool  listsnapshots  off                 default