1. A method of dynamic allocation of non-volatile memory in a cache storage subsystem, comprising: constraining a redundant array of independent disks (RAID) 6 array in an unavailable state, the RAID 6 array having been newly created in the subsystem; destaging data from a write cache to a storage medium to free memory space; reserving the freed memory space for allocation to data-persistent storage; allocating the memory space to an adapter in the subsystem as a target for data in the event of a power loss; and changing the RAID 6 array to an available state.