Method and apparatus for caching data in an solid state disk (ssd) of a hybrid drive that includes the ssd and a hard disk drive (hdd)

A hybrid drive comprising:

• a storage system, wherein the storage system includes
• a hard disk drive having a first data storage capacity, and
• a solid state disk having a second data storage capacity, wherein the second data storage capacity of the solid state disk is lower than the first data storage capacity of the hard disk drive;
• a host interface configured to be in communication with a host processor, the host processor including one or more levels of cache;
• and
• a disk controller coupled to the storage system, wherein the disk controller is configured to access the solid state disk as a final level of cache prior to the disk controller accessing the hard disk drive,
• wherein in response to the host interface receiving a request for data that is not cached in the one or more levels of cache of the host processor, the disk controller is configured to determine first whether the data requested by the host processor is cached in the solid state disk being the final level of cache, and
• (i) retrieve, in response to determining the data requested by the host processor is cached in the solid state disk, the data requested by the processor from the solid state disk, or
• (ii) retrieve, in response to determining the data requested by the host processor is not cached in the solid state disk, the data requested by the host processor from the hard disk drive.