1. A persistent storage device, comprising: persistent storage, comprising a set of persistent storage blocks; NVRAM, comprising a type of nonvolatile storage distinct from the persistent storage and comprising a set of NVRAM blocks; a storage controller configured to receive commands from an external host device and further configured to: in response to a transfer command, transfer data in a specified NVRAM block to a corresponding persistent storage block, wherein the data was previously written to the specified NVRAM block.