HDD having both dram and flash memory

A hard disk drive (HDD), comprising:

• at least one disk storing data;
• at least one Dynamic Random Access Memory (DRAM) device;
• at least one flash memory device;
• and
• at least one disk controller managing data storage by executing logic including, at least in part:
• receiving a write request;
• determining whether the DRAM device is full and if not, writing data to the DRAM device to satisfy the write request;
• otherwise at least some of the time
• determining whether the flash memory device is full, and if not, destaging data from the DRAM device to the flash memory device and then writing data to the DRAM device to satisfy the write request, otherwise if the flash memory device is full spinning up the disk if not already spinning and destaging data from the flash memory device to the disk, then destaging data from the DRAM device to the flash memory device, then writing data to the DRAM device to satisfy the write request.