A method for mirroring and securing of a memory system

A method for controlling a storage system, the first memory means at a first location having a first storage volume, a second storage means at a second location having a second storage volume, and a third storage means at a third location having a third storage volume comprising, wherein the storage devices are connected to each other to communicate with each other, the method comprising the steps of: - storing a copy of data stored in the first storage volume in the second storage volume at a first time; - writing the copy of data written in the first storage volume into the third data storage volume; - storing a write history of data written in the first storage volume as a first differential management table in the third memory means after the first time; and - allowing the third storage device, makes contents of the data stored in the second storage volume consistent with the content ...