root@nas:/home/leo# zpool get expandsize data
NAME  PROPERTY    VALUE     SOURCE
data  expandsize  2.69T     -
root@nas:/home/leo# zpool list data
NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
data  8.12T  6.69T  1.43T     2.69T    41%    82%  1.00x  ONLINE  -
root@nas:/home/leo# zpool status data
  pool: data
 state: ONLINE
status: Some supported features are not enabled on the pool. The pool can
        still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(5) for details.
  scan: resilvered 2.22T in 24h12m with 0 errors on Wed Nov  1 16:43:39 2017
config:

        NAME                                       STATE     READ WRITE CKSUM
        data                                       ONLINE       0     0     0
          raidz1-0                                 ONLINE       0     0     0
            ata-ST4000DM005-2DP166_ZGY0956M-part1  ONLINE       0     0     0
            wwn-0x5000c500a36f4651-part1           ONLINE       0     0     0
            ata-ST4000DM000-2AE166_WDH01SND-part1  ONLINE       0     0     0
        cache
          sdc1                                     ONLINE       0     0     0

errors: No known data errors
root@nas:/home/leo# zpool online -e data ata-ST4000DM005-2DP166_ZGY0956M-part1
root@nas:/home/leo# zpool list data
NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
data  10.9T  6.69T  4.18T         -    30%    61%  1.00x  ONLINE  -
root@nas:/home/leo# zpool get autoexpand data
NAME  PROPERTY    VALUE   SOURCE
data  autoexpand  off     default



See also: https://tomasz.korwel.net/2014/01/03/growing-zfs-pool/