I have 2 units in my house - one on the ground floor, and one in the finished basement. Whenever I've done an update before, there is an outage of several minutes, even though only one AP is offline/rebooting. I vaguely recall seeing a message about updating the configuration or whatever (e.g. it seems like the non-master can't just 'take over' instantly?) This is kind of annoying, as I have to do it at 7AM or some-such when no-one else is up and online...