How to Avoid a Redundant Path to Power Failure

I am not referring to a major utility power failure, just to a common pitfall of power distribution system practice and management. There are several basic, but key, power components in the data center.

1. Utility power source(s) and main power panel(s)
2. Backup generator and ATS (automatic transfer switch)
3. UPS (uninterruptible power supply) and maintenance bypass panel
4. PDU (power distribution unit) (or subpanel from UPS)
5. Rack-level PDU
6. Server’s internal PS (power supply)

A common practice in today’s mission-critical data center environment is to equip servers with dual power supplies for improved reliability. However, if improperly implemented, it could increase the likelihood of power failure.

In a “perfect” scenario, such as a Tier 4 data center, there are two completely independent power paths, each composed of items 1-6. Each path and the items in the path must be capable of supporting 100 percent of the entire data center load by itself. This represents true 2N redundancy, which means that no single point of failure will interrupt the operation of the data center equipment.

Of course, not everyone is fortunate enough to operate a Tier 4 data center. While we would all like to have complete power system redundancy, cost usually forces some trade-offs. While we try to ensure the highest level of system fault tolerance within budget restrictions, this usually means that although servers have dual PSes, there are not two completely independent paths for items 1-5.