When the electrical power fails or decreases to an unacceptable voltage level, a UPS (Uninterpretable Power Supply) device that offers battery backup is used.
Description :
While bigger UPS systems have enough battery for several hours, smaller UPS systems only have power for a few minutes, just long enough to safely shut down the computer.
UPS systems are only employed briefly in mission-critical data centres before electrical generators take over.
When an outage has occurred and the batteries are running low, UPS systems can be configured to notify file servers to shut down properly.