Inside the Building: The Power Chain
Follow a unit of electricity from the transmission line to a processor and you count a surprising number of handoffs: substation, medium-voltage distribution, transformer, switchgear, uninterruptible power supply, distribution unit, rack power supply. Each handoff loses a little energy and adds a place to fail. Redundancy, described in the Uptime Institute's tiers and in the shorthand of N plus one and 2N, is the price paid to make those failures survivable. Faraday's read is that redundancy labels deserve the same scrutiny as any other claim: ask what failure the design survives, whether a third party certified it, and whether the workload inside actually needs that level of protection.
Knowledge check
What is the difference between a concurrently maintainable design and a fault-tolerant design in the Uptime Institute's classification?
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A concurrently maintainable design, Uptime's Tier III, lets any single component or path be taken out for planned maintenance without shutting down the computing load. A fault-tolerant design, Tier IV, also survives an unplanned failure of any single component or path without interrupting the load. The second usually requires fully independent systems and costs more.