Patent ID: 7676641

Claim:
A storage controller comprising: a host write component operable to write a data object to source data image at one of a plurality of controlled storage apparatus; a first copy component responsive to a first metadata state and operable to control copying of said data object to a first target data image at one of said plurality of controlled storage apparatus; a second copy component responsive to a second metadata state and operable to perform a step selected from a group consisting of: controlling copying of said data object to a second target data image at one of said plurality of controlled storage apparatus; and causing said first copy component to perform copying of said second target data image to said first target data image; a third copy component operable to control cascaded copying of said data object to a third target data image at one of said plurality of controlled storage apparatus; wherein one of said second and said third copy components is operable to control cascaded copying of a delimited subsequence of data images responsive to a third metadata state indicating currency of a grain of data in one of said second and said third target data images; and wherein for each grain removed from a source storage apparatus a predetermined number of copies is preserved in the cascade.