info needed-upgrade 8.1 to 10.0 with zfs root

[Gene]

I've got an 8.1 amd64 system that I want to upgrade to 10.0. The system uses 
ZFS including root. Can anyone point me to reliable reading on upgrading - 
the handbook doesn't really get into ZFS and root, thanks -

Bs# gpart show

=>       34  976773101  ad0  GPT  (466G)
         34        128    1  freebsd-boot  (64K)
        162    8388608    2  freebsd-swap  (4.0G)
    8388770  878906250    3  freebsd-zfs  (419G)
  887295020   89478115       - free -  (43G)

=>       34  976773101  ad4  GPT  (466G)
         34        128    1  freebsd-boot  (64K)
        162    8388608    2  freebsd-swap  (4.0G)
    8388770  878906250    3  freebsd-zfs  (419G)
  887295020   89478115       - free -  (43G)

=>       34  976773101  ad6  GPT  (466G)
         34        128    1  freebsd-boot  (64K)
        162    8388608    2  freebsd-swap  (4.0G)
    8388770  878906250    3  freebsd-zfs  (419G)
  887295020   89478115       - free -  (43G)

=>        63  1953525105  da0  MBR  (932G)
          63  1953520002    1  freebsd  [active]  (932G)
  1953520065        5103       - free -  (2.5M)



--