Question came up yesterday in this chat from erson about updating the firmware simultaneously on both CMCs in a chassis. Recommended best practice would be to update only the standby CMC first and then make it active. Not only would that ensure the ability to “roll back” if there’s an issue, it is also less disruptive. But yes, there is an “all” checkbox so you could update both at the same time. And if you do that as erson found out, in addition to losing all connectivity during reboot it’s also like pulling both CMCs from the chassis which causes the fans to go to max as there isn’t any intelligence to say that you don’t need all that cooling. For reference, see page 164 of the User’s Guide http://support.dell.com/support/edocs/software/smdrac3/cmc/cmc2_10/en/ug/pdf/cmcug_en.pdf#page=164