A storage system comprising: - a plurality of storage drives, wherein the storage drives include hard disk drives and solid-state drives; - a cache memory configured to temporarily store data read from or written to a host computer; - a plurality of microprocessor packages, each including at least one microprocessor configured to take charge of volumes, which are provided by the storage system to the host computer; and - a plurality of local memories allocated to the plurality of microprocessor packages respectively, the local memories each provided with a first cache directory holding data caching control information assigned to the allocated microprocessor package; - a shared memory accessible from the microprocessors, the shared memory is configured to store a second cache directory, wherein the second cache directory is a backup information of the first cache directory; wherein - a first microprocessor in a first microprocessor package of the microprocessor packages is configured to update the data caching information in a first cache directory of the local memory of the first microprocessor package and is configured to determine whether or not to update the backup information in the shared memory with the first cache directory; wherein - in response to receiving a read command from the host computer to a first volume, the first microprocessor, which is in charge of the first volume, is configured to update the first cache directory in a first local memory in the first microprocessor package; wherein the storage system further comprises: - a plurality of types of non-volatile storage drives showing different access performance to provide a plurality of volumes; wherein data caching control information hold in the first cache directory in the first local memory and data caching control information in the second cache directory in the shared memory each include data caching control information for a first volume of the plurality of volumes assigned to the first microprocessor, wherein the first microprocessor, which is in charge of a first volume of the volumes, is configured to determine whether to reflect the update of the caching control information in the first local memory to the shared memory, based on the type of the non-volatile storage drives for providing the first volume; and wherein the first microprocessor is configured to determine whether to reflect the update of the caching control information in the first local memory to the shared memory, based on at least any one of a load to the first microprocessor, a load of the cache memory, and a cache hit rate on the first volume. - a plurality of storage drives, wherein the storage drives include hard disk drives and solid-state drives; - a cache memory configured to temporarily store data read from or written to a host computer; - a plurality of microprocessor packages, each including at least one microprocessor configured to take charge of volumes, which are provided by the storage system to the host computer; and - a plurality of local memories allocated to the plurality of microprocessor packages respectively, the local memories each provided with a first cache directory holding data caching control information assigned to the allocated microprocessor package; - a shared memory accessible from the microprocessors, the shared memory is configured to store a second cache directory, wherein the second cache directory is a backup information of the first cache directory; wherein - a first microprocessor in a first microprocessor package of the microprocessor packages is configured to update the data caching information in a first cache directory of the local memory of the first microprocessor package and is configured to determine whether or not to update the backup information in the shared memory with the first cache directory; wherein - in response to receiving a read command from the host computer to a first volume, the first microprocessor, which is in charge of the first volume, is configured to update the first cache directory in a first local memory in the first microprocessor package; wherein the storage system further comprises: - a plurality of types of non-volatile storage drives showing different access performance to provide a plurality of volumes; wherein