Stonewall40,  To eliminate downtime you will update a single CMC and then when it powers down and reboots it will failover to the secondary. Once it does that then update the secondary CMC and it will reboot and fail BACK over to the original CMC.  You don't want to do both as it will down the enclosure. 
Hey! We have an m1000 chassis that is running version 3 firmware and a customer would like to upgrade to the latest. I've read conflicting procedures on doing this. One says update both primary and secondary at the same time and another document saying switch to secondary upgrade it and then switchback upgrade it first CMC. What's the latest wisdom on this? Thanks! Dave  
updating CMC firmware