Planned data center maintenance

We are currently running 6 nodes, 3 at each datacenter, I got an email today telling me they are planning a 30 minute outage, what steps should be done to make sure we do not split brain?

Update, I forgot, I have 4 databases here, and 3 at the datacenter, what happens when the cluster gets cut in half for 15 min? how long on a non busy cluster can I stop mysql so I can still receive an IST instead of SST? My database is currently 30GB so it would be nice to not have to go through that transfer.Would it be best to remove a node from the datacenter, run 4 here, and 2 at the other site?