Patent ID: 8775765

Claim:
A computer system comprising: a storage system, which 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; a first server computer, which is configured to read from and writes to the storage system by the block access protocol and is configured to: as storing files to the first virtual volume, write file name space information indicating names of the files and locations of data of the files on the first virtual volume, and write data of the files to the first virtual volume; delete 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 still data of the certain file are stored in the first virtual volume; and process a 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, and a second server computer, which is configured to: (C2) receive the data of the at least one file from the first server computer; (D) write the data of the at least one undeleted file to a second virtual volume which is different to the first virtual volume, by the block access protocol; and (E) change a single file name space shared by the first and second server computers, 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 one storage system and does not include physical storage area in another storage system.