Patent ID: 8521984

Claim:
A server computer reading from and writing to a storage system by a block access protocol, wherein the storage system is configured to define a virtual pool including a physical storage area of a storage media in the storage system and to provide a first virtual volume using the virtual pool so that the storage system is configured to allocate the physical storage area included in the virtual pool to the first virtual volume upon writing data to the first virtual volume, the server computer comprising: a memory storing a program; and a CPU configured to execute the program for: when files are stored to the first virtual volume, writing file name space information indicating names of the files and locations of data of the files on the first virtual volume, and writing data of the files to the first virtual volume; deleting a certain file in the first virtual volume so that a name of the certain file does not exist in the file name space information but in which data of the certain file is stored in the first virtual volume; and processing capacity reduction of the allocated area in the storage media by: (A) specifying at least one undeleted file indicated by the file name space information; (B) reading data of the at least one undeleted file from the first virtual volume, by the block access protocol; (C) writing the data of the at least one undeleted file to a second virtual volume which is different than the first virtual volume, by the block access protocol, wherein the second virtual volume is created for the capacity reduction using the virtual pool, so that the storage system is configured to allocate the physical storage area included in the virtual pool to the second virtual volume upon writing data to the second virtual volume; wherein the first virtual volume is deleted so that allocated physical storage area of first virtual volume becomes unallocated physical storage area of the virtual pool; and wherein the virtual pool includes the physical storage area in the storage system and does not include a physical storage area in another storage system.