Our rack currently uses 120V UPS units and PDUs, but we've acquired a Dell PowerStore that needs higher-voltage power. The rack also has servers and network switches, and space is tight.
Would it make sense to add separate UPS units for the storage, or replace the rack power setup and move everything to 208V? What should we check before deciding?
For a single rack, I would compare the full replacement cost against adding a separate power setup for the storage. A full conversion may be attractive if the existing UPS units are nearing replacement anyway, or if four units would eat too much rack space.
Include the UPS units, PDUs, circuits, installation, cords and any disruption during the changeover. Higher voltage can improve power supply efficiency, but the savings may be modest, so I wouldn't assume they'll pay for a full conversion quickly.
Start by finding out what power is available at the building and get an electrician involved. In North America, 208V commonly comes from a three-phase system, while 240V is commonly available from split-phase service. A 208V circuit can supply a single-phase load, so the voltage alone doesn't tell you everything about the circuit.
Check the exact PowerStore model's input specifications before buying anything. If it accepts 240V as well as 208V, that may give you another option depending on the service. The electrician can assess the feeds, protection and installation rather than treating this as a plug swap.
Inventory every device before deciding the whole rack can move. Check the input voltage range on each power supply, including the switches, and verify the UPS outputs, PDU ratings, receptacles and equipment cords. Some equipment may need to stay on 120V, even if most of the servers support a wider range.
Also check whether a supported 120V power supply option exists for the exact storage configuration. Don't count on it being available for a high-power unit, but it's worth checking the product documentation before pricing the alternatives.
I'd lean toward a full conversion if rack density is growing. At the same power draw, 208V means less current than 120V, so a suitably rated circuit can deliver more power. That can make future expansion easier and reduce the number of small UPS units and cables to manage.
Just don't budget for a big cooling reduction based on voltage alone. The equipment still needs roughly the same power to do its work. Any reduction in heat would come from actual efficiency gains, not simply from using a higher voltage.
Daro:
And if a few devices only accept 120V, retain a suitable 120V supply or investigate a properly rated step-down transformer rather than assuming everything can use the new PDUs.
Whatever voltage you choose, map out both power paths. For dual-supply equipment, check that each path has enough capacity to carry the required load if the other fails. Two UPS units alone don't guarantee redundancy if they share a point of failure upstream.
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9m~thermostat_42:
Battery runtime and capacity matter too. Two larger UPS units need to support the loads and runtime you actually require, not just fit in the rack.