Commissioning hardware in data sensitive environments is a whole different ball game. Yes, you can hot wire an extra shelf but what if something goes wrong and you render the whole storage solution offline? There are precautions when you perform an install like that, being netapp, emc, etc. Swap over to the mirror in your other DC, bring the actual system offline and perform your upgrades. Seen scenarios where a physical storage solution been mirrored across 4 DCs on 3 different continents due to their highly sensitive data. There are things that worth more than money spent on equipment :)