Hello, are you talking about upgrading the switch firmware or the EQL firmware?  I'm presuming switch firmware.  If you have two LAG'd stacks with connections split between them then restarting each switch stack should cause no issues.  You can move one cable at a time.  Any connections on that link will terminate and the iSCSI initiator will re-login.  Verify that that link is still reachable.  I.e. if you moved an array port, ping that port IP address from server connections on both switches.  Want to make sure that links between switches is working correctly. 
Hi,  I am about to failover the iSCSI traffic running between 6 Esx 4.0 hosts and 1xPS4000 and 1xPS6000. My problem is that the Esx-version don't allow me to change iSCSI login timeout from 5 secs to 60 secs as recommended in the EQL docs. If this would work there wouldn't be a problem to do a controller failover but with this issue I am uncertain if I will lose iSCSI--connections causing some or all of the vm:s to go down when the passive controller becomes active in the "new stack". I have tested to do a "manual failover" by taking a cable at a time from the active controller and connecting it to the "new stack" but this was done on 1xPS6100 and 1xPS4100 that didn't havie any iSCSI connections towards them.  My question is if this is a suitable option even when iSCSI-connections exist on the members or are there any better options?  Your advice is greatly appreciated //Cris
Failing over 1xPS4000 and 1xPS6000 between 2x6224 stacks connected wth LAG to 
be able to do a fw upgrade