Upgrading 8.1 -> 9.x with ZFS root

[Gene]

Hi All: 

 I'm planning to move from my current FBSD 8.1 (amd64) to 9.2. My concern is 
 that i'm using ZFS complete with a zfs root and I need to be sure that I don't 
 manage to screw up root. Can someone point me to some good reading on ths 
 subject - 

 With grateful thanks, 
 Gene 

 And a Merry Christmas (or Happy Holidays) to all

--