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Rack Power

One of the problems we face at Monash it trying to provide resilient power to racks of equipment. We have several hundred racks with 1 to 10 devices in them. These devices have only one power cord, and one power supply each.

The Cisco Catalyst switches do have the option of a separate box providing power via a special connector (protecting against failure of the box's internal power supply rather than against external power feed failure). This however introduces different scaling and provisioning problems ...

One idea would be to supply each rack with two separate power feeds (resiliency through redundancy), and somehow get both power feeds to all devices.

One options is to use a ATS (Automatic Transfer Switch). From the APC website:

APCs Rack Automatic Transfer Switch (ATS), also known as the Redundant Switch, is a high availability switch that has two input power cords, one for each AC line, which provide redundant power to connected equipment. The Rack ATS is designed to supply power to the connected load from a primary AC source. If that primary source becomes unavailable for whatever reason, the Rack ATS will automatically begin sourcing power from the secondary source. The transfer time from one source to the other is seamless to the connected equipment. The Networked units have built-in network connectivity, which allows for remote management via Web, SNMP, or Telnet interfaces.

One problem with the APC products is that their 120V products can have e.g. six or eight outputs for supplying individual devices, but the 230V products have e.g. two or even one unusual output connector. This would then require power strip(s) to distribute power to the individual devices -- yet another box in the rack.

Another problem with the APC equipment is that it isn't cheap. . There are cheaper ATS's that are made for e.g. domestic mains/generator switchover, but I expect that they don't provide seamless switchover. A brief power glitch may cause a switch to reboot -- which may or may not be acceptable.

Another question is whether to provide a UPS in each rack, e.g. resilent power for VoIP phones connected to Power-over-Ethernet switches. A UPS could be connected to one mains feed, or to two feeds via a ATS (I hadn't seen any UPS's that had two input feeds). In the two mains case, a single output from a ATS could be all you need:

two mains == ATS -- UPS -- power board(s) ... switches

Or there could be a big UPS in the bottom of each building providing power to all racks in that building. This UPS could have dual power feeds via a ATS, or each rack could have a ATS to select between UPS and raw mains. ...

[ /monash | # ]