A data storage system incorporating a write-caching subsystem that implements a steady-state media-based cache is described. The steady-state of the media-based cache can be obtained by directing non-sequential write commands and data received from the host device to multiple independent cache locations and, thereafter, selectively copying or moving such data between the caches so that none of the caches are either too full or too empty. In this manner, a non-sequential write command can be cached in a power-safe manner until it is efficient and/or convenient to write such data to the mainstore portion of the physical media.