1. A distribution processing unit of a shared storage in a system comprising: a master server for performing job management; a plurality of two or more slave nodes for executing independent jobs; a shared storage having a plurality of storage media for storing data; a management server for managing the shared storage; and a network connecting these components; wherein a mapping means for dividing one or more LUs (Logical Units) composed of the plurality of storage media into two or more virtual sub LUs is included in the shared storage or in each slave node of the plurality of slave nodes; when a number of divisions of the virtual sub LUs is designated as a parameter for dividing the LUs, the mapping means rearranges the LUs into virtual sub LUs divided into the designated number, and the blocks within the LU are associated with the LU number of the virtual sub LUs and the blocks within the virtual sub LUs having the LU number; when the mapping means is included in each slave node of the plurality of slave nodes, the mapping means of a slave node rearranges the virtual sub LU associated with the LU as the virtual sub LU of the slave node in which it is included, and further associates a given block within the LU with a block within the virtual sub LU of the slave node in which it is included; the management server has a data storage means; and when storing data to the LU, the data storage means connects the slave node having created the virtual sub LU associated with the block within said LU, and stores the storage target data to the LU via the block within the virtual sub LU associated with said slave node.