Abstract: A method, system, computer system and computer program product to synchronize data and a snapshot of the data taken at a given point in time. Persistent data change maps are used to track changes made to data after a snapshot of the data is taken. Changes to the data are tracked using a persistent accumulator map, and changes to the data with respect to a second set of data are tracked using a persistent volume map. The persistent accumulator map is updated with each update of the data. Persistent volume maps are updated when a subsequent snapshot of the data is taken. Only changes to the data made after the snapshot was taken are applied to synchronize the snapshot with the data so that all of the data is not copied. Snapshots can be located in a physically separate location from the data itself.

Abstract: A method, computer program product, computer system and system that enable symmetrical data change tracking with respect to a set of data and a copy of the set of data, referred to as a snapshot or a second set of data. The data and the copy may be independently updated after the two sides are “split.” A join may be performed of the two sides of the split to resynchronize the data. For the first set of data, an accumulator map tracks changes to the first set of data and a volume map tracks changes to the first set of data with respect to a second set of data. For the second set of data (the snapshot), a second accumulator map tracks changes to the second set of data and a second volume map tracks changes to the second set of data with respect to the first set of data.

Abstract: A method, system, computer system and computer program product to maintain consistency between mirrored copies of data. A first data change map identifies regions that are about to be updated. If a system failure occurs during the update, the first data change map identifies regions that were being changed so that only those regions can be synchronized to restore consistency between the mirrored copies of data. A second data change map tracks changes made to data after a snapshot of the mirrored data is taken. This second data change map enables the mirrored copies of data to be synchronized without copying all data from one mirrored copy to another. The first and second data change maps are updated in parallel to reduce processing time and overhead. This parallel processing enables fast restoration and synchronization of mirrored copies of data, while having minimal effect on performance of applications using the data.

Abstract: A method, computer program product, computer system and system that enable symmetrical data change tracking with respect to a set of data and a copy of the set of data, referred to as a snapshot or a second set of data. The data and the copy may be independently updated after the two sides are “split.” A join may be performed of the two sides of the split to resynchronize the data. For the first set of data, an accumulator map tracks changes to the first set of data and a volume map tracks changes to the first set of data with respect to a second set of data. For the second set of data (the snapshot), a second accumulator map tracks changes to the second set of data and a second volume map tracks changes to the second set of data with respect to the first set of data.