In a first system among first and second systems being a duplexed system as a path to a storage device, in a first SAS expander including a first port directly coupled to a storage device, buffer-on signifying that buffering is to be performed by the first SAS expander is configured with respect to the first port. In the second system, in a second SAS expander including a second port directly coupled to the same storage device, buffer-off signifying that buffering is not to be performed by the second SAS expander is configured with respect to the second port. By selecting any of the first system and the second system as a path of a command, whether or not the command is to be buffered by the first or second SAS expander directly coupled to a storage device serving as a destination of the command is determined.