Downtime will be ~5 minutes while it reboots.
But it'll be worth it... we've had way more than 5 minutes of downtime a day lately because of Jesus doing absolutely stupid things. Hopefully this should fix it all up.
In any case, once all users are moved to clusters we won't need such a beefy machine for the master and we can probably find a new creative use for it.
Anyway, too much talk. I'm off with evan to the NOC. We're also racking the 3rd cluster master server. (right now we just have 1 cluster live... and cluster "0")