Patent 7403960 was granted and assigned to Hitachi on July, 2008 by the United States Patent and Trademark Office.
The present invention provides fair use of resources between users by reducing capacity necessary for storage of snapshot differential data. In a storage device system, differences between only those files meeting predetermined conditions are managed as snapshots. Furthermore, upper limits are set for capacity of pools used for each condition, and when the total volume of differential data stored under a certain condition reaches the pool capacity, further snapshots are not created under that condition.