I believe the confusion starts in that we've all been doing server updates the same way for a LONG time. You update the system through your method of choice (ISO, floppy, software tool, etc) then you reboot the server and it's running the new firmware code.
I like to say that the "S" in UCS does NOT stand for "Server", it stands for "System". When you're updating Cisco UCS there's a few more things going on under the covers. First, every compute node (server) under control of Cisco is under the ever watchful eye of the Fabric Interconnects. In order to make these changes, the servers in UCS boot from the FIs and load what is called PNuOS. You might have seen this scroll by when you first configure a Service Profile on a system.
|Cisco UCS PNuOS|
When you make any change to a server under UCS that is disruptive, say for instance a FW update, it says, "OK, I hear what you're saying to me, but I'm going to look to my Maintenance Policy first and get back to you on when I'll actually perform the change you asked."
The default maintenance policy is "immediate" ... yucky, don't ask me, I didn't make it the default. Most people change to at least a "User-Acknowledged" policy. Which means do the change when I acknowledge it at some later time. At this point you should be saying, "So Scott, there's actually two sides to the UCS system ... one where it's under my control, and the other where it's under the FI overlord's control?" Correct. Until you actually acknowledge the changes, the system will never flip the bit in the service profile to make it boot from PNuOS. If you simply reboot the system, it's still just a regular server and will perform a regular server reboot, never booting from PNuOS, but simply doing what you told it as a regular server.
Now when you make a change and have a User-Ack maintenance policy, you'll get a pop up that looks like this:
|Ack the Ack|
To acknowledge the action, you have to Acknowledge it in the pending activities.
|Pending Activities - where you Acknowledge and flip the bit for PNuOS|