This was topic was covered breifly from another post.

http://forum.open-e.com/showthread.p...light=failover

First we do not recommend running different versions of DSS with the auto failover enabled. All updates are safe to perform. You can update Primary or Secondary in any order just make sure that they are in Sync to original position of the Primary.

So if you update the Secondary first then reboot the Primary will state that its Service is running degraded mode (this is normal). Once the Secondary is back up w/ the update then go to the Failover manager and click the start button to failover to the secondary making is Active and perfrom the update to the Primary.