XMission's Company Journal

Improve your server uptime with redundant (A+B) power

While XMission has provided our Colocation customers with the option to get redundant power feeds to their cabinets for years, we’re happy to see much more interest lately. Although the lower cost of deploying multiple power supplies (PSUs) to server hardware in recent years has helped increase adoption, experienced systems administrators all know that PSUs have higher failure rates than most other computer components. Considering how easy and affordable it is to deploy A+B power these days, we strongly recommend that everyone who colocates servers do so.

What is A+B Power?
Fortunately, most data centers provide a relatively simple solution by providing power from separate “buses.” In a nutshell, a power bus is a distinct and isolated portion of the power distribution system in a facility’s electrical infrastructure. For example, XMission has two separate power buses which begin at the point where electricity enters the facility and is split between two ATS (Automatic Transfer Switch) systems. The ATS units monitor utility power and each one automatically turns on our generators during a black out. Each ATS feeds a separate bus with their own UPS (Uninterruptible Power Supply) systems. Each UPS then feeds PDUs (Power Distribution Units) which are evenly distributed across the colocation floor and contain breakers for the individual circuits that service all of the customer cabinets.

Why Redundant Power?
With so many critical systems involved in a data center’s power infrastructure, it’s easy to see how important redundant power buses can be to help ensure uptime for your servers. Since affordable redundant PSUs are readily available for most server chassis equipment now, there’s absolutely no reason not to follow best practices and always buy server hardware which includes them. Most data centers, including XMission, also make A+B power to your cabinet affordable. At XMission, you can in fact have A+B power at no additional charge. If you colocate equipment with us and don’t have A+B power deployed to your cabinet currently, just contact our sales staff. Finally, it’s incredibly easy to upgrade to A+B power since all you need are servers with multiple PSUs and A+B power in your cabinet.

Things to Keep In Mind
To provision for A+B power, you should utilize a pair of identically sized circuits (e.g., 2 x 20 Amps) and power strips. Also be sure to monitor usage so that you never exceed the National Electrical Code (NEC) standard of 80% for those circuits, which is 16 Amps on a 20 Amp circuit. Ideally, you want to evenly distribute usage on each circuit, which is an average of 40% per power strip. In the event of a power outage on either bus, everything simply fails over to the other circuit. No complex configurations required.

Switching to A+B power is among the easiest and most affordable upgrades you can perform to improve server uptime. PSUs can fail, circuit breakers can trip, or a UPS or generator might have a problem during a power outage, even when preventative maintenance is rigorously followed. In the end, power is not only essential to your servers working but a data center’s power infrastructure has a number of potential points of failure. Since N+1 redundancy is always a good idea, be sure you include electricity in that equation and sleep better at night.


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