Hot swap and hot spare revisited.

There are three levels of hot-something hardware repair capability in a storage system
  1. cold swap
  2. hot swap
  3. hot spare

differing on two properties
  1. if a downtime is required to perform the repair
  2. if a human intervention is required

Hence, the levels break down as follows:
  1. Cold swap: both downtime and human intervention required
  2. Hot swap: human intervention is required but no downtime
  3. Hot spare: no downtime and no human intervention

The price of the system increases with the level of hotness, while the maintenance cost decreases. In certain applications, where the maintenance cost is high, it is cheaper to put in enough "hot spare" parts for the entire useful life of the system than to use a hot-swap and human intervention. While an unmanned spacecraft is the extreme example of the high-cost maintenance, we will probably see maintenance-free end-user systems soon after hard drive production finally comes back to proper rates.


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