Abstract: A head assembly forming a field replaceable unit (FRU) is assembled and adjusted such that head-to-tape path alignments are accurately made completely independently of an associate tape drive device. The head assembly includes an aluminum base having a magnet and shield assembly attached to a back thereof. A head is attached to a rigid beam with a voice coil formed thereon and the head and beam are flexibly attached to the base with the voice coil functionally located for movement within the magnet assembly. A flag on the beam is sensed by an optical sensor attached to the base such that a horizontal position of the head can be sensed. An azimuth arm is attached to the front of the base having an azimuth and penetration datum affixed thereto. The azimuth arm is moved horizontally in relation to a mount plate of a data cartridge for azimuth adjustment. The penetration datum is adjusted for the penetration alignment relative to the mount plate.

Abstract: A data storage system provides disaster recovery capability by asynchronously transmitting record updates to a secondary site in sequence consistent order. Such record updates are stored at a primary site in a cache memory of a storage controller. A circular queue is created having a head pointer for locating a first (or oldest) record update with subsequent record updates of a track being linked therefrom in sequence consistent order. A tail pointer of the circular queue points to the last record update. A counter field is provided in a track slot header for counting a number of updated records in the track and hence the circular queue. When a data mover in the host processor at the primary site reads record updates for transmission to the secondary site, the data mover starts with the record update pointed to by the head pointer such that the data mover moves through the circular queue (and hence the record updates) in a backward chain fashion.

Abstract: A remote copy system incorporates dynamically modifiable ports on the storage controllers such that those ports can operate either as a control unit link-level facility or as a channel link-level facility. When configured as a channel link-level facility, a primary storage controller can appear as a host processor to a secondary storage controller. The primary storage controller can thereafter initiate multiple request connects (RQC) concurrently for servicing a single I/O request. In this manner, a first available path can be selected and system throughput thus improved since RQCs so not need to be sent serially from path to path looking for an available path.

Abstract: A method and system for controlling data flow in a storage subsystem containing multiple cache and/or multiple NVS elements based on the operability of the cache arrays and NVS arrays. In a data processing system having a storage controller connecting a plurality of host processors and a plurality of storage devices, this invention provides a method and architecture for managing multiple storage elements within the controller, without a degradation in subsystem performance and without data integrity problems. A set of configuration registers is utilized by the microcontroller to direct cache and NVS access to the proper storage array. A configuration table is loaded with status information concerning the memory arrays at Initial Microcode Load(IML) and this information is periodically updated during controller operation.

Abstract: A storage system improves error debugging by directing distributed system components associated with an error condition to temporarily suspend data processing for collecting failure information. The collected failure information is correlated for later analysis according to an issued diagnostic state save channel command word (CCW) that is triggered by the detection of said error condition. The storage system includes a host processor running applications generating record updates. A data mover in the host processor issues the diagnostic state save CCW upon receiving an error code from one of the system components. The failure information includes software, hardware and microcode control structures of the distributed system components.

Abstract: A remote data shadowing system provides synchronous, storage based, real time disaster recovery wherein a secondary site is located remote from the primary site. An error recovery program at the primary site quiesces applications running thereat for performing error recovery procedures and signalling both primary and secondary locations that failed duplex has occurred. The error recovery program determines the cause of failed duplex, and if error recovery is successful, duplex mode is resumed. If the error recovery program is unable to perform error recovery successfully, then further write updates at the primary site are prohibited and an error message is communicated to operators at both the primary and secondary sites.

Abstract: A method and apparatus for improving storage controller throughput and reducing unit control block contention when selecting a Utility Volume for servicing non-specific read requests. Throughput is increased by enabling the storage controller to service non-specific read requests issued against a Utility Volume which is not the same as the device associated with the data that the non-specific read is requesting. The Utility Volume is dynamically selected by considering the current loads on the available devices for both specific and non-specific processing. A Penalty Index is assigned to each volume, wherein the Penalty Index is a weighted average of the specific and non-specific processing. The device having the lowest Penalty Index is selected as the Utility Volume for a session. A Penalty Index evaluation is made at a Reference Point which is further enabled by a random clock to ensure that sessions do not likely pick the same Utility Volume.

Abstract: An automated storage system uses a pass-through picker assembly interposed between a storage device and a plurality of storage cells, wherein the pass-through picker assembly is mounted on an accessor and incorporates independently operating fore and aft grippers driven by a single motor. The fore and aft grippers are tandemly mounted such that the fore gripper can be aligned to one of a plurality of storage cartridges located with the storage cells, and the aft gripper can be aligned with a storage slot of the storage device. The pass-through picker design allows the fore gripper to grasp a storage cartridge, feed the cartridge through to the aft gripper, release, and then allow the aft gripper to grip and pass the storage cartridge to the storage slot. In this way, a special priority cell of the storage cells, directly across from the storage slot, can very quickly pass a priority storage cartridge directly to the storage device without moving the pass-through picker assembly.

Abstract: A gear constructed of a monolithic material having a first reflectivity and having one or more projections is interlocked into a cam constructed of a monolithic material having a second reflectivity substantially different from the first reflectivity. The one or more projections are mated with corresponding one or more openings in the gear whereby such mating provides a torsional lock. A reflective sensor having a focal length corresponding to either a surface of the projections or a surface of the cam detects positions of the gear by transitions from reflective to non-reflective surfaces and vice versa. The detected transitions are used to provide feedback control to a motor driving the gear.

Abstract: Primary and secondary data processing systems are coupled via a communication system. Data storage in both systems is provided by a log structured array (LSA) system that stores data in compressed form. Each time data are updated within LSA, the updated data are stored in a data storage location different from the original data. Selected data recorded in a primary data storage of the primary system is remote dual copied to the secondary system for congruent storage in a secondary data storage, such as for disaster recovery purposes. The primary systems creates a remote copying session. Within such remote copying session, a series of "pending write update" sessions are ESTABLISHED. All data updated within each pending write update session is a consistency group of data. Within each pending write update session update data are retentively stored in both the primary and secondary systems (such as in a non-volatile cache).

Abstract: A magneto-resistive (MR) head includes protection from electrostatic discharge without introducing additional processing steps. The MR sensor comprises a soft film biased (SFB) magnetic read sensor sandwiched between two high resistivity magnetic materials. The MR sensor is located between two MR shields wherein each MR shield is connected to an MR sensor ground signal lead by a resistor. The resistor is constructed from the high resistivity magnetic material such that the resistor is deposited at the same process step as the MR sensor.

Abstract: A pass-thru cassette magazine performs several functions beyond vertically holding a plurality of data cassettes in a position randomly accessible to a data storage subsystem picker assembly, including locking the data cassettes within corresponding storage cells in either an import or export position when the magazine is not interfaced to the storage subsystem (that is during handling by an operator). The "locked" position indicates that a data cassette cannot be removed from the magazine without a force of approximately one kilogram or greater. When a magazine is interfaced to the storage subsystem, the magazine is interlocked thereto such that the magazine cannot be removed without releasing the interlock. While the magazine is interlocked, the lock on the data cassettes is disabled so that the data cassettes can be freely picked by the picker assembly or removed or inserted by an operator.

Abstract: An automated storage system transports data cartridges between a storage device and a plurality of storage cells via a picker assembly. The storage cells are formed of one or more removable magazines. The picker assembly accurately locates each data cartridge within a storage cell by first establishing a zero position reference and locating a home position relatively therefrom. The home position is a predetermined point on each magazine. An infrared detector and infrared sensor are situated on the picker assembly for precisely locating the home position. Each cartridge is known to be located within a predetermined tachometer count range from the home position. The detector/sensor is used to precisely locate each cartridge. The precise tachometer position is stored and the cartridge is returned to the known location. As a result, tolerance accumulation effects are eliminated in the system.

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 head guide assembly of a tape device includes a beam for securely mounting a tape head thereon, wherein the tape head is accurately aligned and mounted so as to have both an improved resonance response as well as isolation from external shock or vibrations. A head guide support, made from a super gusseted material, supports the beam and tape head wherein the beam is mounted on a brass base for reducing resonances. The brass base is coupled to the head guide support via a kingpin and wedge clamps for locking the tape head in alignment without affecting the alignment. Additional resonances in a direction of a pitch of the tape head is reduced by further connecting the brass base to the head guide support without distorting the aligned position of the brass base. Shock mounts are provided for floating the head guide assembly from a base of the tape device.

Abstract: A remote data shadowing system provides storage based, real time disaster recovery capability. Record updates at a primary site cause write I/O operations in a storage subsystem therein. The write I/O operations are time stamped and the time, sequence, and physical locations of the record updates are collected in a primary data mover. The primary data mover groups sets of the record updates and associated control information based upon a predetermined time interval, the primary data mover appending a prefix header to the record updates thereby forming self describing record sets. The self describing record sets are transmitted to a remote secondary site wherein consistency groups are formed such that the record updates are ordered so that the record updates can be shadowed in an order consistent with the order the record updates cause write I/O operations at the primary site.

Abstract: A method and apparatus for improving storage controller throughput when servicing non-specific read requests. Throughput is increased by enabling the storage controller to service non-specific read requests issued against a device address which is not the same as the device address associated with the data that the non-specific read is requesting. The device address associated with the data is thus free to be used for another I/O operation. When the device address used by the non-specific read is a non-busy type (that is, the device and/or data is not locked) then the throughput improvement is obtained by increasing the number of data requests that may be concurrently handled by the storage controller.

Abstract: Memory system for internally rearranging fields in database records. The memory is separated into modules, each module separately addressable. Each memory module is addressed by selectively modifying a supplied address, for example by the output from exclusive-OR gates, having inputs from the address supplied to the memory system and another inputs from address modification registers. The address modification registers are selectively set by the external utilization device to permit reading different rows in the memory modules, The data output columns from the memory modules can be rearranged using selector devices such as demultiplexors. Data can be masked by precluding certain selector control signals.

Abstract: A method and apparatus for accurately locating targeted append points in a tape drive. The effects of interlayer slip (ILS) are eliminated and smaller IBGs are possible thus providing increased data capacity for a given tape cartridge. A coarse tachometer count is used in combination with the read dataflow to accurately locate the proper append point even with a small IBG size. The appended data are assured to be written using the proper tape velocity which virtually eliminates improper write appends and read temporary errors previously caused by ILS effects. The solution also guarantees that customer data previously written to the tape are not accidentally overwritten.

Abstract: The average time a user must wait to have an object retrieved from an automated optical disk library is reduced by a method for prioritizing read requests. When a read request is received it is added to a queue of pending requests. All pending requests associated with volumes currently mounted on optical disk drives are processed first. The pending requests associated with the opposite sides of the currently mounted volumes are processed next. The next requests to be processed are those pending read requests associated with the unmounted volume having the greatest number of pending read requests. Thereafter any other pending requests for that unmounted volume will be processed as normally would be done for a currently mounted volume. This method continues until all pending read requests have been processed for the unmounted volumes.