zpool-upgrade —
    manage version and feature flags of ZFS storage
    pools
  
    zpool | 
    upgrade [-V
      version]
      -a|pool… | 
  
  zpool upgrade 
  - Displays pools which do not have all supported features enabled and pools
      formatted using a legacy ZFS version number. These pools can continue to
      be used, but some features may not be available. Use
      
zpool upgrade
      -a to enable all features on all pools (subject to
      the -o compatibility
    property). 
  zpool upgrade
    -v 
  - Displays legacy ZFS versions supported by the this version of ZFS. See
      zpool-features(7)
      for a description of feature flags features supported by this version of
      ZFS.
 
  zpool upgrade
    [-V version]
    -a|pool… 
  - Enables all supported features on the given pool.
    
If the pool has specified compatibility feature sets using the
        -o compatibility property,
        only the features present in all requested compatibility sets will be
        enabled. If this property is set to legacy then no
        upgrade will take place.
    Once this is done, the pool will no longer be accessible on
        systems that do not support feature flags. See
        zpool-features(7)
        for details on compatibility with systems that support feature flags,
        but do not support all features enabled on the pool.
    
      -a 
      - Enables all supported features (from specified compatibility sets, if
          any) on all pools.
 
      -V
        version 
      - Upgrade to the specified legacy version. If specified, no features
          will be enabled on the pool. This option can only be used to increase
          the version number up to the last supported legacy version
        number.
 
    
   
The following command upgrades all ZFS Storage pools to the
    current version of the software:
# zpool upgrade -a
This system is currently running ZFS version 2.