A computer-implemented method according to one embodiment includes managing a cache in a tiered data storage system. The cache is configured to be powered by a temporary power source during a power loss event. The managing includes determining an amount of time that the temporary power source is capable of powering the cache before the temporary power source is depleted, and maintaining a dynamic cache size. The maintaining includes dynamically selecting the cache size based on the amount of time that the temporary power source is capable of powering the cache before the temporary power source is depleted, and based on a latency of destaging extents of data in the cache.