ZFS pool - HEALTH fault

[James B. Byrne]

Immediately following an upgrade from FreeBSD-11.1 to 11.2p4 we
received the following warning.  I can see the suggested remedy but I
need to know why this has happened first.  We have previously upgraded
numerous hosts from FreeBSd-11.1 to 11.2, all of which are using zfs,
and no other system has reported such a fault,

 ZFS pool - HEALTH fault

NAME    SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP
HEALTH  ALTROOT
zroot   296G   182G   114G        -         -    55%    61%  1.00x
ONLINE  -

  pool: zroot
 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(7) for details.

  scan: scrub repaired 0 in 6h1m with 0 errors on Sun Nov 18 07:01:32
2018

config:

        NAME        STATE     READ WRITE CKSUM
        zroot       ONLINE       0     0     0
          vtbd0p3   ONLINE       0     0     0

errors: No known data errors


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James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
Harte & Lyne Limited          http://www.harte-lyne.ca
9 Brockley Drive              vox: +1 905 561 1241
Hamilton, Ontario             fax: +1 905 561 0757
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