Redundant Power Supplies, a Path to Failure?
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Overview: 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 a as a Tier 4 Data Center, there are 2 completely independent power paths, each comprised of items 1-6. Each path and the items in the path must be capable of supporting 100% 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 Power Supplies, there are not two completely independent paths for items 1-5.
The more common scenario is two rack level PDUs and that (hopefully) each of the server's PS cords are plugged into a different PDU. This creates a "sense" of redundancy for most administrators. In reality, this is where the hidden exposure to power problems starts.