Abstract:
An apparatus, method, computer readable medium and logical device have been created for storing essentially only modified or changed information from one of a pair of mirrored storage devices. In one exemplary embodiment, essentially only tracks of information from a primary volume of a mirrored pair of mirrored storage units, which have been modified since creation of the mirror, need be stored. In another exemplary embodiment, essentially only tracks of information from a primary volume of a mirrored pair of mirrored storage units, which have been modified since a last resynchronization, need be stored. In yet another exemplary embodiment, essentially only tracks of information from a primary volume of a mirrored pair of mirrored storage units, which have been modified since a last command, need be stored. By storing actual information which was modified and by storing essentially only information which was modified, a small amount of actual information need be stored. In addition, such information can be stored on the same storage unit as, or on a storage unit separate from, one or more of the primary and secondary volumes. As such, recovery of information can occur quickly. Only necessary information need be recovered; recovery can occur quickly; and/or recovery can occur in either a forward or backward direction.