In our test vCenter environment, we have one ESXi host connected to one dual controller PS6000 EqualLogic array. We were curious how bad the interruption would be in a single member pool, so we tested it. In a single member pool or if you are short of room, using a maintenance pool is not an option. We do this in production and there is indeed no interruption whatsoever, using a maintenance pool works well. Once the member is evacuated, update it, reboot it, and put it back into the production pool, and move to the next array. Depending on how much you have to move this may take a few hours or overnight. When you assign a member array to the Maintenance Pool, the volumes on that array will migrate to the other member(s) of your production pool. If you have more than one array, and at least the largest array’s worth of free room, then the official way to do a firmware update is to use a “Maintenance Pool”. As most operating systems have a disk timeout value of 30 seconds or longer, no one really notices. This takes something like 27 seconds (26969 ms).
Eager readers want to know if EqualLogic array firmware upgrades are non-disruptive, so we tested it in our mighty remote environment! Bottom line: The firmware update process halts I/Os during cut-over from one controller to the other.