How To Use beadm to Upgrade FreeBSD installed in a ZFS Boot Environment, with minimal downtime

Changing to the New Boot Environment

Your almost done, all that's left is to change to the new boot environment. This is a simple command followed by a reboot, and the point at which your only downtime occurs. 

# beadm activate 10.1-RELEASE-p3-r276159-2015.01.09
Activated successfully

I like to follow this up with a beadm list to verify everything before rebooting. 

# beadm list
BE                                 Active Mountpoint  Space Created
install                            N      /          875.6M 2015-01-02 13:56
10.1-RELEASE-p3-r276159-2015.01.09 R      -            1.7G 2015-01-09 12:13

Note:  The Active Column is key here, it shows that currently the install boot environment is active, and that the new environment, 10.1-RELEASE-p3-r276159-2015.01.09, will be activated at reboot.

Reboot and Done. 

shutdown -r now

Note:  of course you should verify that everything is functional after the reboot.