1. A computer-readable, non-transitory storage medium storing a load balancing program for use in a storage system including a plurality of storage nodes interconnected by a network and storage devices coupled to each storage node, the load balancing program, when executed on a computer, causing the computer to execute a procedure comprising: storing management data describing association between logical segments and physical segments, wherein the logical segments are virtual storage areas with a specified segment size into which a logical volume is divided, and wherein the physical segments are real data storage areas with the specified segment size into which storage space of the storage devices is divided; identifying, responsive to access requests directed to an access range of the logical volume, the physical segments associated with the logical segments in the specified access range of the logical volume, based on the management data; subdividing the logical segments in the access range into logical sub-segments with a specified sub-segment size, as well as the physical segments associated therewith into physical sub-segments with the specified sub-segment size; remapping the logical sub-segments to the physical sub-segments according to a predetermined remapping algorithm in such a way that the physical sub-segments corresponding respectively to different logical sub-segments of a single logical segment are to be distributed in different physical segments; and executing the access requests based on the remapped logical sub-segments and physical sub-segments, wherein: the remapping uses a pair of parameters, one parameter serving as a segment number to designate a logical segment or a physical segment, the other parameter serving as a sub-segment number to designate a logical sub-segment or a physical sub-segment, the remapping algorithm converts a first pair of parameter values to a second pair of parameter values according to a predetermined conversion rule, and the remapping associates a logical sub-segment designated by the first pair of parameter values with a physical sub-segment designated by the second pair of converted combinations.