Abstract: A method to control access to logical volumes. The method provides a plurality of host computers and an information storage and retrieval system comprising a plurality of logical volumes. The method forms (N) host computer groups, assigns one or more of the host computers to the (i)th host computer group, such that each host computer assigned to (i)th host computer group is not assigned to any other of the (N) host computer groups. The method forms (N) logical volume groups, assigns one or more logical volumes to the (i)th logical volume group, such that each of the logical volumes assigned to the (i)th logical volume group is not assigned to any other of the (N) logical volume groups. The method maintains a database associating the (i)th host computer group with the (i)th logical volume group, and permits a host computer assigned to the (i)th host computer group to access a logical volume assigned to the (i)th logical volume group.

Abstract: A method to control access to logical volumes disposed in an information storage and retrieval system using parallel access volumes. The method provides an information storage and retrieval system comprising a plurality of logical volumes, and a plurality of host computers, where each host computers is capable of communicating with the information storage and retrieval system. The method creates a parallel access volume having an alias, and persistently associates that parallel access volume with an original base logical volume, where the original base logical volume may be assigned to one of (N) logical volume groups. If the original base logical volume is assigned to the (i)th logical volume group, the method permits each host computers assigned to the (i)th host computer group to access the original base logical volume, or the current base logical volume, associated with the parallel access volume.

Abstract: An error recovery process for a non-synchronous DASD control unit. A channel process within the control unit is able to operate on different fields from a device process within the control unit. Independent errors may be sensed by each process. The error recovery process provides for restarting only the trailing process and deferring handling of the error sensed by the leading process, whenever possible.

Abstract: A method and system for enhancing the efficiency of data accessing within a storage subsystem which is coupled to a host system via a storage subsystem controller and a data channel. The storage subsystem controller preferably includes a tracked cyclic storage device which has multiple disks which are rotatable about a single spindle. Recording tracks within each disk are then accessed utilizing multiple switchable transducer heads. A signal transmitted from the host system is utilized to define a sequence in which a group of recording tracks are to be accessed. That signal is then utilized to create a transducer head switching table within the storage subsystem controller which lists each recording track to be accessed and an associated control parameter for selecting a particular transducer head to be utilized to access a subsequent recording track.

Abstract: A cached DASD peripheral subsystem is operated in a so-called non-synchronous mode, that is, device operations are not synchronous to the host processor operations. A rate-changing buffer is interposed between the channel attachment for the host processor and the DASD, preferably having a storage capacity for one full DASD track of data. The rotational position for the data records being transferred in either direction, i.e., write or read, are kept in the rate-changing buffer to be kept with the record being transferred through the rate-changing buffer. Each time the peripheral subsystem supplies ending status to the host processor and all records to be transferred are retentively stored in DASD, a record control field and the rotational position of the last record transferred in a chain of commands being transferred the rotational position of such last record, its type, and other control data are stored in a control store separate from any cache directory or track directory in cache.

Abstract: A control unit for DASD operation to transfer data between the device and a buffer and between a channel and a buffer. In that manner the channel and device are enabled to transfer data independently of each other. Mechanisms are provided for communication between the channel interface process in the control unit and the device interface process in the control unit. Some of these mechanisms are stored with the record in the buffer and others are stored in control storage. Principle communicating mechanisms include a device record pointer, a channel record pointer, a next operation field, a device state indicator, record control flags, and two buffer pointers.