Patent ID: 7409507
Filing Date: 2008-08-05
Classification: G06F

Abstract:
1. A difference bit map management method for managing a difference of a volume corresponding to a logical volume in a storage apparatus by using a difference bit map to record a difference, which manages renewal with respect to data stored in a logical volume at a certain time point, wherein said difference bit map is expressed by a combination of two-tier tables having an entry of a first tier table and an entry of a second tier table, the entry of said second tier table having a plurality of first bits stored therein; setting a value of one of the first bits to express a presence or absence of the difference shown by the entry of said first tier table; storing in the entry of said first tier table first identification information that specifies the entry of said second tier table and second identification information that indicates an existence or non-existence of the entry of said second tier table; and recording the non-existence of the entry of the second tier table in the second identification information stored on the corresponding entry of the first tier table when all the first bits of the entry of said second tier table are equal to a predetermined value.