1. A storage apparatus comprising: a disk drive having a storage medium for storing a plurality of data sets; and a disk controller configured to control the disk drive, wherein the disk controller comprises: a host interface configured to receive an I/O request from a host system; a disk interface operatively connected to the disk drive; and a cache mechanism operatively connected to the host interface and the disk interface and having a first cache memory configured from a volatile memory and a second cache memory configured from a nonvolatile memory, wherein the disk controller is configured to manage a plurality of attribute values each associated with the plurality of data sets stored in the disk drive, wherein the disk interface writes one or more first data sets specified from the plurality of data sets stored in the disk drive into the second cache memory based on the plurality of attribute values, and wherein, in accordance with a backup request, the disk controller transfers a second data set specified from the first data sets written in the first cache memory to the second cache memory.