1. A storage system, comprising: a memory array comprising a plurality of non-volatile solid-state storage devices; and a controller configured to write data to, and read data from, the memory array in response to commands received from a host system, and being capable of purging a variable number of said solid-state storage devices in parallel; wherein the controller implements a command set that enables the host system to initiate a purge operation in which the memory array is purged, and to control how many of the solid-state storage devices are purged at a time during the purge operation, such that both an amount of time and a current level used to perform the purge operation are controllable by the host system.