Data Center Power Availability is More Than a Number

by James Leach
04 January 2013

It can be difficult to appreciate the differences between data center power delivery architectures. Every data center provider you talk with has a power story to tell and most of them sound pretty good. The challenge is selecting the power architecture that is right for you.

One way to compare power delivery systems is to look at overall availability. Availability is usually expressed as a percentage of the total time the system is expected to be running. This is where the number of 9’s come in. You might find availability percentages of three 9’s (99.9%), four 9’s (99.99%), etc.

While a number might make you feel better at night, it won’t necessarily keep the phone from ringing. I suggest you look for three words when evaluating data center power delivery systems: Redundant, Distributed, and Scalable.

Redundant – multiple independent systems

This is the "N" you hear so much about in data centers. Basically, N is the amount of a component that you need to deliver a service. For example, you need one power path from the utility to your server rack. This path could include multiple pieces of equipment including a main switchboard, backup generator, UPS (uninterruptible power supply), and a PDU (power distribution unit). A second independent power path with all of those elements to the same server rack would be 2N. If there is a break in the first path, then the second path takes over. Ask your data center provider how they design for redundancy in all critical systems. The most fault tolerant way to keep your system running is to have multiple N’s. The challenge is that too many N’s can be expensive to acquire and complicated to manage.

Distributed – a resource pool + backup(s)

This is the "+1" in an N+1 design or the "+2" in an N+2 design. When the costs of the redundant architecture become prohibitive, a distributed approach for critical elements of the infrastructure is a great way to improve overall system reliability. You take a device and set it up as a spare for the required pool of devices. Say you need five UPSs to run the pod and you have one additional UPS that can backup any of the five in the pool – that’s N+1. Two spares for the pool means N+2. The critical element of this configuration is the monitoring and management system that must recognize a device failure and automatically switch to the back-up device.

Scalable – engineered for growth and change

Data centers are continually growing and changing all at the same time. To deliver superior service at an affordable price, the data center should be built out based on usage. The shell may be in place day 1, but the power and cooling should be purchased and installed as customers move in. Otherwise you are paying too much, too soon. Also, within the IT cages, servers, storage devices, and network gear are being added, removed, upgraded, and relocated. Your data center needs to be engineered for both growth and change. Power and cooling systems should accept additional devices as capacity requirements grow. Live IT power load should be dynamically shared or moved across the entire facility. All of this must occur without an outage.

Ragingwire data center - 100% power availabilityAt RagingWire, we’ve coined a name for our redundant, distributed, and scalable power deliver architecture – we call it 2N+2. We have two patents on the technology and offer a 100% Availability SLA (service level agreement) with these configurations.

How can we be so confident that with our 2N+2 architecture your power will not go down? We have 2N redundancy on the power paths to your cage or rack and an N+2 distributed design for the critical elements in the power delivery system. Lastly, one of our patented inventions is a unique cross-facility power switching fabric and a massively scalable topology that allows us to move, share, and scale live IT power load throughout the data center without requiring a maintenance outage.

For data centers, the old adage definitely still applies: "You can’t manage what you don’t measure." Availability numbers are a great metric to manage your data center power delivery system. However, when choosing the right data center colocation solution, be sure to look for power delivery systems that are redundant, distributed, and scalable.

James Leach

Vice President, Marketing