The invention provides a technique for improving processing performance of I/O commands in a storage system in which ownership of each LU is introduced. The storage system includes: a disk device having storage regions that are managed as a plurality of logical units; a plurality of processors that process read commands to the disk device; and a cache that the processors can use to process the read commands. An owner processor that is in charge of processing to each logical unit is allocated to each logical unit. When decision is made that dirty data is not present in the cache in a target region of the read command, there are a case where the owner processor of a logical unit that includes the target region processes the read command, and a case where a non-owner processor, as the processor other than the owner processor, processes the read command.