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 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 plurality of addressable data storage devices are selectively directly accessed or accessed via a cache memory. Access via the cache memory uses one of a plurality of logical addresses; each of the data storage devices is represented by a plurality of the logical addresses. Each of the data storage devices can be reserved for direct access; such reservation does not apply to device accesses via the cache. Accesses to the devices are queued on a device basis.

Abstract: Data associated with a defective area of a backing store and stored in an alternate area, such as defective and alternate tracks in a direct access storage device, is selectively stored in a high speed buffer front store based upon usage of such data. A first replacement control governs buffer operation for data from good areas of the backing store, and a second independent replacement control governs buffer operation for data from alternate storage areas. Limitations are imposed on the amount of data subject to the second replacement control.

Abstract: Direct access storage devices (DASD) are connected to a host via a cache. Each device can be independently addressed by any one of a plurality of addresses, also termed logical devices and exposures. Since operations between DASD and cache are combined for all of the independent logical devices, resetting operations related to one independent logical device can inadvertently interfere with operations of another independent logical device. To maintain data integrity, a programmed control accommodates logical device independence by using queues and control blocks relating to the DASD and logical devices, respectively.