My vote is for one at a time :) I have always heeded this notice in the Upgrade docs;
**Caution You must perform the Cisco Unified CallManager installation serially; that is, on one server at a time. After you reboot the server and after you verify that the server pulled the subscription from the publisher database server, you can begin the upgrade on the next server.
From this section;
Upgrading the Cisco Unified CallManager Subscriber Server(s)
You know, it's always that one line I cant find in the documents. I had that doc open and couldnt find the statement that I *thought* I saw one day. Oh well. long upgrade this weekend then with 5 servers. ugg.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.