Abstract: Load balancing of activities on physical disk storage devices is accomplished by monitoring reading and writing operations to blocks of contiguous storage locations on the physical disk storage devices. A list of exchangeable pairs of blocks is developed based on size and function. Statistics accumulated over an interval are then used to obtain access activity values for each block and each physical disk drive. A statistical analysis leads to a selection of one block pair. After testing to determine any adverse effect of making that change, the exchange is made to more evenly distribute the loading on individual physical disk storage devices.

Abstract: A data storage facility for transferring data from a data altering apparatus, such as a production data processing site to a remote data receiving site. The data storage facility includes a first data store for recording each change in the data generated by the data altering apparatus. A register set records each change on a track-by-track basis. A second data store has first and second operating modes. During a first operating mode the second data store becomes a mirror of the first data store. During a second operating mode the second data store ceases to act as a mirror and becomes a source for a transfer of data to the data receiving site. Only information that has been altered, i.e., specific tracks that have been altered, are transferred during successive operations in the second operating mode. Commands from the local production site initiate the transfers between the first and second operating modes.

Abstract: A method for operating a magnetic disk storage device in read/write and read-only modes. A control program in a system cache memory receives write requests for transferring data to a logical volume. The control program determines whether the write request is directed to a track that is in a read/write or read-only operating mode. Only requests to tracks having a read/write operating mode are enabled to continue. A system administrator or user controls the operating modes for each track in the disk operating system.

Abstract: A method and apparatus for communicating a plurality of commands from a first device to a second device over a data communication link coupling the first and second devices, the plurality of commands including at least a first command and a second command. The first and second commands are transmitted over the data communication link from the first device to the second device in a single data transmission such that only a single propagation delay through the data communication link is incurred in transmitting both the first and second commands over the data communication link.

Abstract: Two data storage systems are interconnected by a data link for remote mirroring of data. Each volume of data is configured as local, primary in a remotely mirrored volume pair, or secondary in a remotely mirrored volume pair. Normally, a host computer directly accesses either a local or a primary volume, and data written to a primary volume is automatically sent over the link to a corresponding secondary volume. Each remotely mirrored volume pair can operate in a selected synchronization mode including synchronous, semi-synchronous, adaptive copy-remote write pending, and adaptive copy-disk. Direct write access to a secondary volume is denied if a “sync required” attribute is set for the volume and the volume is not synchronized. If a “volume domino” mode is enabled for a remotely mirrored volume pair, access to a volume of the pair is denied when the other volume is inaccessible.

Abstract: The invention relates generally to mass storage systems, and in particular to mass storage systems in which stored logical volumes are duplicated in mirrored form. The system includes a method for dynamically adjusting the mirror service policy for a disk drive system by periodically collecting statistics describing the reading and writing of data to mirrored logical volumes of the system in successive time periods and determining, from time to time, from the collected statistics, whether the mirror service policy should continue or should change. In particular, the system takes into account activity levels at the physical devices and results in more efficient accessing of logical volume pairs as well as a better balance of loading and accessing the logical volumes.

Abstract: A system and method for providing on-line, real-time, transparent data migration from an existing storage device to a replacement storage device. The existing and replacement storage devices are connected as a composite storage device that is coupled to a host, network or other data processing system. The replacement storage device includes a table which identifies data elements that have migrated to the replacement storage device. When a host system makes a data transfer request for one or more data elements, the replacement storage device determines whether the data elements have been migrated. If the data elements have migrated, the replacement storage device responds to the data transfer request independently of any interaction with the existing storage device. If the data elements have not migrated, the replacement storage device migrates the requested data elements and then responds to the data request and updates the data element map or table.

Abstract: A data network with data storage facilities for providing redundant data storage and for enabling concurrent access to the data for multiple purposes. A first data processing system with a first data facility stores a data base and processes transactions or other priority applications. A second data storage facility, that may be physically separated from the first data storage facility, mirrors the data in the first data storage facility. In a concurrent access operating mode, the second data storage facility makes the data available to an application concurrently with, but independently of, the operation of the other application. On completion of the concurrent operation, the second data storage facility can reconnect with and synchronizes with the first data storage facility thereby to reestablish the mirroring operation.

Abstract: A data network with a remote data facility for providing redundant data storage and for enabling concurrent access to the data for multiple purposes. A local data processing system with a data facility stores a data base and processes transactions or other priority applications. A second system, physically separated from the first system includes the remote data facility that normally mirrors the data in the first system. In an independent access operating mode, the second system is enabled to operate on the data within its data facility concurrently with, but independently of, the operation of the first system. On completion of the independent operation, the second system reconnects with and synchronizes with the first system thereby to reestablish the mirroring operation of the second system.

Abstract: Two data storage systems are interconnected by a data link for remote mirroring of data. Each volume of data is configured as local, primary in a remotely mirrored volume pair, or secondary in a remotely mirrored volume pair. Normally, a host computer directly accesses either a local or a primary volume, and data written to a primary volume is automatically sent over the link to a corresponding secondary volume. Each remotely mirrored volume pair can operate in a selected synchronization mode including synchronous, semi-synchronous, adaptive copy--remote write pending, and adaptive copy--disk. Each write request transmitted over the link between the data storage systems includes not only the data for at least one track in the secondary volume to be updated but also the current "invalid track" count for the secondary volume as computed by the data storage system containing the corresponding primary volume.

Abstract: Two data storage systems are interconnected by a data link for remote mirroring of data. Each volume of data is configured as local, primary in a remotely mirrored volume pair, or secondary in a remotely mirrored volume pair. Normally, a host computer directly accesses either a local or a primary volume, and data written to a primary volume is automatically sent over the link to a corresponding secondary volume. Each remotely mirrored volume pair can operate in a selected synchronization mode including synchronous, semi-synchronous, adaptive copy--remote write pending, and adaptive copy--disk. A number of automatic and non-automatic recovery mechanisms are provided on a logical volume basis for a desired level of data integrity and degree of operator or application program involvement. If a "volume domino" mode is enabled for a remotely mirrored volume pair, access to a volume of the pair is denied when the other volume is inaccessible.

Abstract: A method and apparatus for interfacing two ESCON compatible devices over a communication channel that is not dedicated solely to ESCON communication, such as a public communication network or links, for example, a T1 or T3 line. The devices may include a master storage device and a mirroring storage device disposed at remote locations. In one embodiment, the devices communicate using the ESCON protocol. In other embodiments, the devices communicate using modified versions of the ESCON protocol that have a reduced number of handshakes to improve performance.

Abstract: A mirrored memory for a data processing system. The memory system includes two device controllers and related disk drives for storing the mirrored data. Each of the disk drives is divided into logical volumes. Each device controller contains a plurality of reading processes and a correspondence table that establishes the reading process to be used in retrieving data from the corresponding disk drive. Each disk controller responds to a read command that identifies the logical volume by using the correspondence table to select the appropriate reading process and by transferring data from appropriate physical storage device containing the designated logical volume.

Abstract: A method and apparatus for interfacing two ESCON compatible devices over a communication channel that is not dedicated solely to ESCON communication, such as a public communication network or links, for example, a T1 or T3 line. The devices may include a master storage device and a mirroring storage device disposed at remote locations. In one embodiment, the devices communicate using the ESCON protocol. In other embodiments, the devices communicate using modified versions of the ESCON protocol that have a reduced number of handshakes to improve performance.

Abstract: A data processing network including a local system and a geographically remote system. Each of the local and remote systems includes a data storage facility. The remote data storage facility mirrors the local data storage facility. In a normal operating mode, the local and remote systems operate in near synchronism or in synchronism. In an alternate operating mode, writing operations at the local system immediately update the storage devices in the local data storage facility. Transfers of corresponding data to the remote data storage facility are made independently of and asynchronously with respect to the operation of the local system.

Abstract: Two data storage systems are interconnected by a data link for remote mirroring of data. Each volume of data is configured as local, primary in a remotely mirrored volume pair, or secondary in a remotely mirrored volume pair. Normally, a host computer directly accesses either a local or a primary volume, and data written to a primary volume is automatically sent over the data link to a corresponding secondary volume. The host computer sends chains of channel commands to the data storage system containing a primary (R1) volume of a remotely mirrored volume pair. In order to more effectively use the capacity of the data link, the data storage system containing the primary (R1) volume bundles the write data for all write commands in the chain into a single write command for transmission over the data link to the secondary data storage system containing the secondary (R2) volume.

Abstract: A method and apparatus for transferring data from a donor storage device to a target storage device in parallel with requests from a host computer for transfers between the host computer and the target storage device. A copy subroutine operates in response to background and foreground mode controllers. The background mode controller normally copies data from an initial position in the donor storage device sequentially by data block. When a DTR command from the host processor requests a data element from a block that has not migrated to the target storage device, the foreground controller uses the copy subroutine to transfer the designated block. The storage areas are divided into statistical blocks. If a threshold number of consecutive DTR commands accesses a particular statistical block, the system resets the parameters for the background mode controller to effectively move the copy subroutine to begin background copying from the statistical block.

Abstract: Two data storage systems are interconnected by a data link for remote mirroring of data. Each volume of data is configured as local, primary in a remotely mirrored volume pair, or secondary in a remotely mirrored volume pair. Normally, a host computer directly accesses either a local or a primary volume, and data written to a primary volume is automatically sent over the link to a corresponding secondary volume. Each remotely mirrored volume pair can operate in a selected synchronization mode including synchronous, semi-synchronous, adaptive copy remote--write pending, and adaptive copy--disk. Each write request transmitted over the link between the data storage systems includes not only the data for at least one track in the secondary volume to be updated but also the current "invalid track" count for the secondary volume as computed by the data storage system containing the corresponding primary volume.

Abstract: A data network with a remote data facility for providing redundant data storage and for enabling concurrent point-in-time backup operations. A local data processing system with a data facility stores a data base and processes applications. A second system, physically separated from the first system, includes a data facility that normally mirrors the data in the first system. In a backup mode, the second system is enabled to transfer data from its data facility to a backup facility concurrently with, but independently of, the operation of the first system. On completion of the backup operation, the second system reconnects with and synchronizes with the first system thereby to reestablish the mirroring operation of the second system.

Abstract: A mass storage system having a storage controller connnecting a plurality of host computers to an array of disk drives provides a method and apparatus for propagating a reset command from the host computer to other host computers. The storage controller is used as the intermediary. When the host computers connect to the storage controller using standard bus protocols, certain commands such as a reset command can have profound effects on the storage system, but are not adequately communicated to other host computers connecting to the storage controller over separate bus channels. The storage controller either passes such reset commands to the other host computers or enables the other host computers to sense and request an updated status report from the storage controller indicative of a change in storage configuration or operation.