Patent ID: 7774572

Claim:
A distributed storage system communicatively connected to at least one data processing unit, comprising: a plurality of storage units made to store data and including a storage unit different in maximum available total capacity from the others; control modules each connected to each of said storage units for controlling access to each of said storage units; association means for associating logical storage areas, from/in which data is to be read/written by the data processing unit, with physical storage areas on said storage units; monitor means for monitoring information related to a total volume of data stored in each of said storage units or in all said storage units; index value calculating means for calculating an index value for each of said storage units on the basis of the information related to said total volume monitored by said monitor means; and location means for distributively locating or relocating said logical storage areas in said physical storage areas on said plurality of storage units through said control modules on the basis of said index values calculated by said index value calculating means to carry out distributive location/relocation processing according to the information related to said total volume, wherein said monitor means monitors a usage rate of the entire storage system, which is a ratio of said total volume of data stored in all said storage units or a stored data volume in each of said logical storage areas on all said storage units to a maximum available total capacity of all said storage units, said index value calculating means calculates said index values on the basis of said usage rate of the entire storage system monitored by said monitor means, said location means carries out distributive location/relocation of the logical storage areas to equalize said index values calculated by said index value calculating means, and wherein said index value calculating means calculates, as each of said index values, a difference between a value obtained by multiplying the maximum available total capacity of each of said storage units by, as a weight, the usage rate of the entire storage system monitored by said monitor means and a total volume of data stored in each of said storage units or a stored data volume in each of said logical storage areas on each of said storage units, said total volume or said stored data volume being monitored by said monitor means.