Cold Spare and Cold Swapping
The term cold spare refers to a component, such as a hard disk, that resides within a computer system but requires manual intervention in case of component failure. A hot spare will engage automatically, but a cold spare might require configuration settings or some other action to engage it. A cold spare configuration will typically require a reboot of the system.
The term cold spare has also been used to refer to a redundant component that is stored outside the actual system but is kept in case of component failure. To replace the failed component with a cold spare, the system would need to be powered down.
Cold swapping refers to replacing components only after the system is completely powered off. This strategy is by far the least attractive for servers because the services provided by the server will be unavailable for the duration of the cold-swap procedure. Modern systems have come a long way to ensure that cold swapping is a rare occurrence. For some situations and for some components, however, cold swapping is the only method to replace a failed component. The only real defense against having to shut down the server is to have redundant components residing in the system.