Personally i would do the following. 1. Upgrade the new array first 2. Put new array in its own storage pool 3. Move the volumes over to the new array 4. Upgrade Old array 5. Merge the two arrays into one pool (basically move the new array into the default pool) That would leave you with no need to down guests or esxi servers at all. It can be done completely transparent. if you have any questions let me know
Environment: m1000e with six 710HD Blades - two blades are esxi hosts managed by a guest VM vCenter Server. The remaining 3 blades are Oracle Virtual Servers. All connect to the Equallogic. The only other server which has an iSCSI connection to the Equallogic group is a Symantec Media server.  In the next week or two we'll be adding a Equallogic 6010e to our group. We only have one other Equallogic, so after the installation of the 6010e this will make it a multi-member group. One of the things that needs to be done is updating the firmware on both arrays.   The way I would accomplish this is first:  1. Shutdown all guests, including the vCenter server 2. Shutdown All ESXi hosts (we only have two) 3. Disconnect the iSCSI connection that the Symantec Media server has to the equallogic manually with the Windows iSCSI initiator. 4. Connect to the PS Group Manager and update the firmware.  In step 2 I would like to know if there is another way to disconnect the iSCSI connections with vSphere besides shutting down the hosts? 
Shutdown Equallogic in vSphere5.0 environment