Abstract: An apparatus and program storage device for maintaining data is provided that includes receiving primary data at a first node, receiving mirrored data from a second and third node at the first node, and mirroring data received at the first node to a second and third node.

Abstract: A method for maintaining data is provided that includes receiving primary data at a first node, receiving mirrored data from a second and third node at the first node, and mirroring data received at the first node to a second and third node.

Abstract: An apparatus and method to check integrity when handling data. The method provides a storage array which includes a plurality of sectors. The method defines (N) data state identifiers and (N) parity state identifiers. The method receives a command to handle data, where that command designates a target sector. The method determines the data state identifier assigned to the target sector, determines the parity state identifier assigned to the target sector, and compares the data state identifier and the parity state identifier. If the method determines that the data state identifier and the parity state identifier are the same, the method performs the command to handle data. Alternatively, if the method determines that the data state identifier and the parity state identifier differ, the method generates an error message.

Abstract: An apparatus and method to check integrity when handling data. The method provides a storage array which includes a plurality of sectors. The method defines (N) data state identifiers and (N) parity state identifiers. The method receives a command to handle data, where that command designates a target sector. The method determines the data state identifier assigned to the target sector, determines the parity state identifier assigned to the target sector, and compares the data state identifier and the parity state identifier. If the method determines that the data state identifier and the parity state identifier are the same, the method performs the command to handle data. Alternatively, if the method determines that the data state identifier and the parity state identifier differ, the method generates an error message.

Abstract: A system that enables pipelining of data to and from a memory includes multiple control block data structures which indicate amounts of data stored in the memory. An input port device receives and stores in memory, data segments of a received data message and only updates status information in the software control blocks when determined quantities of the data segments are stored. An output port is responsive to a request for transmission of a portion of the received data and to a signal from the input port that at least a first control count of data segments of the received data are present in memory. The output port then outputs the stored data segments from memory but discontinues the action if, before the required portion of the received data is outputted, software control blocks indicate that no further stored data segments are available for outputting.

Abstract: An adaptive hierarchical cache management system for improving effective cache hit ratios by eliminating unnecessary duplicate cache entries in two coupled cache memories. When a cached Storage Controller (SC) is coupled to a Cached Storage Drawer (CSD), the hierarchical coupling of the SC cache memory and CSD cache memory unnecessarily duplicates cache entries during normal operation. A Conditional Purge procedure purges duplicate lines from the CSD cache subject to a DASD activity threshold. A Prenotify Intent parameter allows the SC to request restaging of the purged cache entry preparatory to fast write or LRU demotion in the SC cache. The new procedures substantially and transparently improve the combined caching efficiency without significant new hardware or software overhead.

Abstract: A computing system includes plural nodes that are connected by a communications network. Each node comprises a communications interface that enables an exchange of messages with other nodes. A ready queue is maintained in a node and includes plural message entries, each message entry indicating an output message control data structure. The node further includes memory for storing plural output message control data structures, each including one or more chained further monrtol data structures that define data comprising a message or a portion of a message that is to be dispatched. Control data structures that are chained from an output messsage control data structure exhibit a sequence dependincy. A processor is controlled by the ready queue and enables dispatch of portions of the message designated by an output message control data structure and associated further control structures.

Abstract: Often in DASD subsystems, circumstances can occur which prevent the full transfer of the required data from channel to subsystem during a write operation. The disclosed methods prevents this data from later being read and treated as valid data by the host processor. This is achieved by marking data as invalid within the storage subsystem once it is determined that a channel error has occured. Subsequently, upon reading that data, the host processor can be made aware of the data invalidity and treat the data accordingly. In a second embodiment, invalid data is discarded rather than stored over the previous valid version of the data, before it is ever stored on DASD.

Abstract: A method and system for efficiently accessing desired datasets among multiple datasets which are stored at specific data addresses within multiple storage subsystems which are coupled to a host system via a storage subsystem controller and a data channel. A data request is transmitted from the host system to the storage subsystems via the data channel. The data request specifies non-address attributes for desired datasets, such as boundary addresses for large data extents including many datasets or a request for all datasets modified since the occurrence of a specified event. The data request is then processed at the storage subsystem controller to determine a data address for each dataset within the storage subsystem which possess the desired attributes. Thereafter, the desired datasets are transmitted via the data channel to the host system in association with a specific address for each dataset.

Abstract: A method and system are disclosed for permitting high concurrency of access during backup copying of designated data stored within a storage subsystem which includes multiple storage devices coupled to the data processing system via a storage subsystem control unit having subsystem memory therein. Data within each storage device is accessed utilizing a Unique Control Block (UCB), which identifies a selected storage device, and an associated data retrieval command sequence which identifies the data to be accessed. Portions of the data copied to subsystem memory within the subsystem storage control unit as sidefiles from a first storage device may be accessed utilizing a Unique Control Block (UCB) associated with an alternate storage device by associating a selected data retrieval command sequence therewith which identifies the data as stored within the subsystem memory.

Abstract: A method and system are disclosed for enhanced efficiency of backup copying of designated datasets stored within a plurality of storage devices coupled to the data processing system via a storage subsystem control unit having subsystem memory therein. Application execution within the data processing system is temporarily suspended long enough to form a dataset logical-to-physical system address concordance to be utilized to administer copying of the designated dataset. Thereafter, application initiated updates to uncopied portions of the designated datasets are temporarily deferred until sidefiles of the affected portions of the designated datasets are written to subsystem memory. The updates are then written to the storage subsystem. Portions of the designated datasets are then accessed and copied from the storage subsystem on a scheduled or opportunistic basis utilizing selected data retrieval command sequences.

Abstract: A technique is described for performing a fast write operation. A host write request, which would normally be serviced by an immediate physical write to a data storage device, is instead written to cache and nonvolatile storage in the data storage device controller. Then, the controller signals the host that the write operation is complete and does not update the physical data storage device until later. A journal log is also used to provide recovery capability in the event of system failure. This technique provides high performance for the units' operation while assuring integrity by keeping two copies of the write operation until the physical update transpires.

Abstract: Data supplied to a data storage system by a host processor has one of two use status. A first use status is that the supplied data is to be retentively stored in the data storage system. A second use status is that the supplied data is exempted from the retentive storage requirement. An example of exempted use status is that data only temporarily stored in the data storage system, i.e. is transitory. A second example is data that is being manipulated prior to retentive storage, data that is temporarily volatile. Termination of the exempted use status results in either discard or a retentive storage of the exempted use data. Data integrity controls for the exempted use status data are described. The invention is described for a data storage hierarchy environment having a volatile cache and a magnetic recorder as a backing store. The exempted use data need be stored only in or primarily in the cache while retentive data is primarily stored in the retentive store and selectively in the cache.

Abstract: The disclosure relates to demotion of data to a backing store (disk storage apparatus--DASD) from a random access cache in a peripheral data storage system. A cache replacement control list, such as a least recently used (LRU) list is scanned in a soon-to-be replaced first portion (portion closest to LRU entry) to identify first data to be demoted. Then the control list is scanned in first and second portions to identify further data to be demoted with the first data as a single group of data. In DASD, such data is all storable in the same cylinder of the DASD.

Abstract: In a multiunit data processing system, such as a multicontrol unit peripheral data storage system, a least busy one of the units requests work to be done from a busier unit. The busier unit, a work sending unit, supplies work to the work requesting or least busy unit. Work thresholds in the respective units determine when work is to be requested or transferred. In a data storage environment, the transferred work consists of data transfers to be achieved usually asynchronously to connected host activities, such as data transfers between a backing and a front store in a data storage hierarchy.

Abstract: A so-called "roll mode" technique provides block transfer with a disk-type of direct-access data-storage device (DASD). A set of chained commands for accessing record areas enables rapidly accessing a plurality of records within a given DASD cylinder of tracks. The rotational position of the surfaces is checked. The command within the chain, irrespective of its location, having the closest logical rotational proximity to the instant rotational position of the surfaces is selected as the first command in the chain. The chain is executed beginning at the indicated rotational position selected command through the end of the chain and then wrapped to the beginning of the original chain and continuing on until the command immediately preceding the rotational position selected command has been executed.

Abstract: Data supplied to a data storage system by a host processor has one of two use status. A first use status is that the supplied data is to be retentively stored in the data storage system. A second use status is that the supplied data is exempted from the retentive storage requirement. An example of exempted use status is that data only temporarily stored in the data storage system, i.e. is transitory. A second example is data that is being manipulated prior to retentive storage, data that is temporarily volatile. Termination of the exempted use status results in either discard or a retentive storage of the exempted use data. Data integrity controls for the exempted use status data are described. The invention is described for a data storage hierarchy environment having a volatile cache and a magnetic recorder as a backing store. The exempted use data need be stored only in or primarily in the cache while retentive data is primarily stored in the retentive store and selectively in the cache.

Abstract: Fast and slow channels are attached to a cached peripheral storage system, having a front store and a backing store preferably with a plurality of data storage devices. The peripheral data storage device data transfer rate is not greater than the data rate of the fast channels but greater than the data rate of the slow channels. For data associated with a fast channel, data promotion from the backing store to the front store is designed to encourage read hits while discouraging write hits. For the slow channel, all data goes through the front store. Cache bypassing controls are handled through the LRU (least recently used) replacement algorithm for the slow channels. A common demotion of data from the front store to the backing store is used for all channels. Front store occupancy varies in that buffering for slow channels (data rate change) tends to store and keep full tracks, while caching for fast channels limits data occupancy.

Abstract: Data is promoted from a backing store (disk storage apparatus termed DASD) to a random access cache in a peripheral data storage system. When a sequential access bit is sent to the storage system, all data specified in a read command is fetched to the cache from DASD. If such prefetched data is replaced from cache and the sequential bit is on, a subsequent host access request for such data causes all related data, up to a predetermined maximum, not yet read to be promoted to cache.

Abstract: A peripheral system attached to a host having plural virtual machines accommodates the virtual machines via "guest" attribute signals signifying that a given chain of peripheral or I/O commands are virtual machine sourced (GO bit). The attribute signals may include modifier control signals to enable the peripheral system to adjust to virtual machine operations of the host. In particular, virtual machine "minidisks" are accommodated.