Can you update one half of the cluster to a newer version of open-e dss and then failover and upgrade the other half?
This is certainly a question I wish to explore as well - having the ability to pull 1/2 of a iSCSI active/standby-system out of production for maintenance (even if it were a manual failover) with no loss what so ever of access to LUN users (esp. ESX hosts etc). Another options being explored in another thread (tho rather poorly by me!), is now to do this more cost effectively, so the standby system is lower rated that the primary (normally ok in DR situations). Cheers.