Abstract: A method for creating a duplicate copy of a tape in which a first tape having a first data set name and a second tape having a second data set name are allocated. Data is written to the first and second tapes so that block for block, the data is located at the same position on each of the tapes. After data is written to one of the tapes, a check is made to verify that the data was written correctly. If an error is detected in writing the second tape, an error flag is set that indicates a copy of the first tape needs to be made. At various stages of the process, checks are made to determine if error flag is on. If the error flag is detected, writing the second tape is suspended.

Abstract: A procedure for the optimal processing of variable-cost actions such as encountered in the storage reclamation procedures for a multivolume data library. The procedure introduces a temporary processing queue to minimize idle processing capacity during the scanning and sorting of a large plurality of variable-cost actions such as the recycling of a plurality of data storage volumes each having a variable recycle processing cost related to the action of valid data remaining on the volume. Volumes (actions) are selected for the immediate queue according to a dynamically-adjusted threshold test for the processing cost. This processing cost threshold is dynamically adjusted to optimize the immediate queue in relation to the available processing capacity. After scanning and sorting all volumes according to recycle processing cost, the temporary (immediate) queue is updated to a final recycle processing queue by appending a sorted deferred queue to the remainder of the immediate queue.

Abstract: An adaptive data transfer channel providing means for a data management access method (AM) to define the channel subsystem data block transfer size and to transfer an extended data block (EDB) by a single channel transfer command to avoid repeated channel command word (CCW) command decode and status presentation operations. The adaptive scheme of this invention is transparent to the user and downwardly compatible with existing data record storage formats because it is independent of the user application program. The host software in the central processing complex (CPC) tests the peripheral data storage device (PDSD) to ensure compatibility with the EDB CCWs before selecting the channel program (CP) to be used for data block transfer in the subchannel. In the EDB format, the PDSD microcode permits the accumulation of logical data blocks (LDBs) from storage to form a single large EDB before transfer to the CPC responsive to a single transfer command.

Abstract: An adaptive data transfer channel providing means for a data management access method (AM) to define the channel subsystem data block transfer size and to transfer an extended data block (EDB) by a single channel transfer command to avoid repeated channel command word (CCW) command decode and status presentation operations. The adaptive scheme of this invention is transparent to the user and downwardly compatible with existing data record storage formats because it is independent of the user application program. The host software in the central processing complex (CPC) tests the peripheral data storage device (PDSD) to ensure compatibility with the EDB CCWs before selecting the channel program (CP) to be used for data block transfer in the subchannel. In the EDB format, the PDSD microcode permits the accumulation of logical data blocks (LDBs) from storage to form a single large EDB before transfer to the CPC responsive to a single transfer command.

Abstract: A method for efficiently utilizing data recording media in a data processing system performing data compression beneath the level of the host processor is disclosed. To improve the ability of a recording media to be copied without increasing host processor overhead, the control unit which sees the compressed data is checked only upon recording a predetermined amount of uncompressed data. At such time, a compression ratio is calculated for the current data set and is used to monitor the recording of the remaining data of the current data set in compressed form. When a predetermined amount of compressed data is estimated to be recorded, the predetermined amount being the minimum storage capacity of a recording media, recording begins on a new recording media.

Abstract: A system for balancing the loads on channel paths in a digital computer during long running applications is disclosed. Only the load associated with relatively long running applications is monitored. For each volume of data eligible for processing, the selection of volumes is first made from those having affinity to the calling host. The load across the respective connected channel paths is calculated. The calculation is weighted to account for the different magnitudes of load resulting from different applications and to prefer the selection of volumes connected to the fewest unused channel paths such that processing of the selected volume will maintain the maximum number of unused channel paths. The optimal volume is selected as the next volume to be processed. The monitored load on each channel path is then updated to include the load associated with the newly selected volume, assuming that the load associated with processing the volume is distributed evenly across the respective connected channel paths.

Abstract: An apparatus for efficiently utilizing data recording media performs data compression beneath the level of the host processor is disclosed. To improve the ability of a recording media to be copied without increasing host processor overhead, the control unit which sees the compressed data is checked only upon recording a predetermined amount of uncompressed data. At such time, a compression ratio is calculated for the current data set and is used to monitor the recording of the remaining data of the current data set in compressed form. When a predetermined amount of compressed data is estimated to be recorded, the predetermined amount being the minimum storage capacity of a recording media, recording begins on a new recording media.

Abstract: Mounting volumes (tape reels or disks) to data processing system is managed for reducing the number of mounting operations. A data accumulation algorithm generates mounting criteria.

Abstract: A storage-management program, executable in one host or simultaneously in a plurality of hosts, manages concurrently executing migration, recall, and recycle (such as defragmentation) tasks. Accesses to data storage volumes (tape, disks, etc.) are managed in accordance with predetermined contention resolution procedures and priorities. Certain tasks are non-interruptible.

Abstract: A storage-management program, executable in one host or simultaneously in a plurality of hosts, manages concurrently executing migration, recall, and recycle (such as defragmentation) tasks. Accesses to data storage volumes (tape, disks, etc.) are managed in accordance with predetermined contention resolution procedures and priorities. Certain tasks are non-interruptible.

Abstract: Allocation of space of peripheral storage devices to host processes is based upon free or unallocated space in each such device. The device, irrespective of capacity, having the largest free space is most likely to receive a next space allocation. A central record in a multi-host system stores free space indications. In a disk storage device free space is indicated by the number of unallocated data storage record tracks for each such device.