Patent ID: 7873809

Claim:
A method of operating an information system, comprising: storing data to a first volume and mirroring the data to a second volume, said second volume being a virtual volume having a plurality of logical storage addresses, wherein a segment of physical storage capacity is allocated for a specified logical address as required when the data is to be stored to said specified logical address; selecting segments of the second volume during a de-duplication operation on the second volume; calculating a hash value for a particular segment representative of data contained in the particular segment; comparing the calculated hash value with previously-stored hash values for other segments in the second volume; linking the particular segment to another segment having a previously-stored hash value that matches the calculated hash value of the particular segment; releasing the particular segment from the second volume when another segment has a previously-stored hash value that matches the calculated hash value of the particular segment, whereby physical storage capacity required for the second volume is reduced; resynchronizing the data stored on said second volume with the data stored on said first volume; splitting said second volume from mirroring said first volume prior to said step of selecting segments of the second volume during the de-duplication operation on the second volume; and reverse synchronizing the data stored on said first volume with data stored on said second volume, wherein before reverse synchronizing whether the second volume has been de-duplicated or not is checked and if the second volume has been de-duplicated, said reverse synchronizing is conducted on to the first volume from the de-duplicated volume.