Unfortunately, the answer is: It depends.  It depends on which upgrade and from what version you are upgrading from.  Some can be done rolling, while others require a simultaneous cluster wide reboot.  A good rule of thumb would be that all major upgrades require a simultaneous reboot while minor ones can be done rolling.  There are exceptions.  Hope that helps.  Cheers, Matt
The upgrade guides seem to be written with mistake and 7x clusters don't have a clear Web GUI upgrade path. Is CLI the only option at this point?  From the OneFS 7.0.2 Upgrade Guide (only upgrade guide on support.emc.com) [URL]  See screenshot of missing data... Is there a path for upgrading Mavericks clusters?[IMAGE]
upgrade in 7+