Abstract: A pair of operationally independent disk drive array data storage subsystems are used to emulate one or more physical devices shared between two control modules. The storage control units of the two data storage subsystems are interconnected by at least one data link to exchange control and data signals therebetween. The storage control units of both data storage subsystems are synchronized to maintain identical virtual device images of certain assigned virtual devices both of the data storage subsystems wherein the duplicated data records of the single virtual device are stored. The data records are therefore stored in available memory on both of the two data storage subsystems. Data is exchanged over the data link to maintain consistency of the two sets of mapping tables.

Abstract: A disk drive array data storage subsystem maps between virtual and physical data storage devices and schedules the writing of data to these devices. The data storage subsystem functions as a conventional large form factor disk drive memory, using a plurality of redundancy groups, each containing n+m disk drives. The use of a pool of r shared spare disk drives in this system is enhanced by apparatus which predicts the exhaustion of the pool of spare disk drives and automatically reorders additional disk drives to replace failed disk drives in the data storage subsystem. The spare disk drive replacement scheduling system records disk drive failure data and extrapolates past failure events to a target date at which the pool of spare disk drives will be exhausted. This exhaustion date is then modified by a reorder and restocking time interval indicative of the time it takes for a repairperson to be dispatched to replace the failed disk drives and replenish the pool of shared spare disk drives.

Abstract: This apparatus makes use of a disk drive array to store data records for an associated host processor. This disk drive array emulates the operation of a large form factor disk drive by using a plurality of interconnected small form factor disk drives. These small form factor disk drives are configured into redundancy groups, each of which contains n+m disk drives for storing data records and redundancy information thereon. The use of this configuration is significantly more reliable than a large form factor disk drive. However, in order to maintain compatibility with host processors that request the duplex copy group feature, the phantom duplex copy group apparatus of the present invention mimics the creation of a duplex copy group in this dynamically mapped data storage subsystem using a disk array and a phantom set of pointers that mimic the data storage devices on which the data records are stored.

Abstract: The deleted dataset space release system provides facilities in a dynamically mapped virtual memory data storage subsystem to immediately release the physical space occupied by a deleted dataset for use by the data storage subsystem to store subsequently received data files. This system also provides data security by preventing the unauthorized access to the data of scratched data files, both in cache memory and on the data storage devices. The deleted dataset space release system utilizes a user exit in the host processor data file scratch routine to transmit information to the data storage subsystem indicative of the host processor data file scratch activity. Existing channel command words are used in a manner that is transparent to the host processor. The data storage subsystem thereby immediately receives an indication that the host processor is scratching a data file from the volume table of contents of a virtual volume.

Abstract: A disk storage system that writes multiple copies of records directed to user-specified volumes. A plurality of spaced apart control units interconnected by direct data links and a corresponding plurality of sets of recording means communicate over the direct data links when a write request is received by one control unit to cause one volume in each set of recording means to write a copy of the received record.