Solaris 10 10/08 Release: The zfs upgrade command is included in this release to provide future ZFS file system enhancements to existing file systems. ZFS storage pools have a similar upgrade feature to provide pool enhancements to existing storage pools.
# zfs upgrade This system is currently running ZFS filesystem version 3. All filesystems are formatted with the current version.
File systems that are upgraded and any streams created from those upgraded file systems by the zfs send command are not accessible on systems that are running older software releases.