Abstract: The system, devices, and methods disclosed herein relate to online data expansion in disaster recovery enabled data storage systems. We disclose embodiments that allow storage devices, which are coupled to one another in a disaster recovery, data replication-type scenario, to perform storage expansion in most cases without having to disable remote replication during the expansion. The teachings of this patent application facilitate methods of expansion for data storage device pairings where the data storage devices are the same size or where the primary storage device is smaller than the secondary storage device. In both of these situations, expansion occurs without disabling disaster recovery. In the situation where the secondary storage device is larger than the primary device, expansion is allowed, with the caveat that disaster recovery must be disabled briefly.

Abstract: Ordering data writes includes at least some of a group of local storage devices receiving a first plurality of data writes, waiting for all of the local storage devices to be ready to switch cycles and causing a coordinated and synchronized cycle switch after all of the local storage devices are ready to switch cycles by sending a first command to each of the local storage devices where the first plurality of data writes are associated with a particular cycle on each local storage device in the group. Ordering data writes also includes at least some of the group of local storage devices receiving a second plurality of writes after initiating the coordinated and synchronized cycle switch where all of the second plurality of writes are associated with a cycle different from the particular cycle on each local storage device.

Abstract: A computer-implemented method of ordering data writes includes at least some of a plurality of primary storage devices receiving a first plurality of data writes and causing a cycle switch for the plurality of primary storage devices. The first plurality of data writes are associated with a particular cycle on each primary storage device in the plurality of primary storage devices. At least some of the plurality of primary storage devices receive a second plurality of writes after initiating the cycle switch. All of the second plurality of writes are associated with a cycle different from the particular cycle on each of the plurality of primary storage devices.

Abstract: Recovering data provided in chunks to a plurality of secondary storage devices includes, for each of the secondary storage devices, discarding data corresponding chunks for which all data thereof has not been received, and, for each of the secondary storage devices, restoring a chunk of data thereto where all of the chunks of data restored to the plurality of secondary storage devices correspond to a particular transmission cycle of primary storage devices that provide data to the plurality of secondary storage devices. Recovering data may also include, following discarding and prior to restoring, for each of the plurality of secondary storage devices having two different chunks, waiting for external intervention to indicate whether to restore a particular one of the chunks. The external intervention may be provided by a host computer that is proximate to at least one of the secondary storage devices or may be provided by a host computer that is proximate to at least one of the primary storage computers.

Abstract: Ordering data writes includes at least some of a group of primary storage devices receiving a first plurality of data writes, causing a cycle switch for the group of primary storage devices where the first plurality of data writes are associated with a particular cycle on each primary storage device in the group, and at least some of the group of primary storage devices receiving a second plurality of writes after initiating the cycle switch where all of the second plurality of writes are associated with a cycle different from the particular cycle on each primary storage device. Writes to the group begun after initiating the cycle switch may not complete until after the cycle switch has completed. Ordering data writes may also include, after completion of the cycle switch, each of the primary storage devices of the group initiating transfer of the first plurality of writes to a corresponding secondary storage device.

Abstract: A data-mirroring method in which, while an I/O process is processing a first I/O request for writing data to a first device, control is obtained from that I/O process executing on a host computer. A second I/O request, this one for writing the data to the second device, is then created. Then, control is returned to the I/O process by causing the first I/O request to be made available to a first data storage system managing the first device.