Abstract: Determining device characteristics includes obtaining a first globally accessible value, if the first globally accessible value corresponds to a stored first value, obtaining device characteristics data from a relatively fast memory, if the first globally accessible value does not correspond to the stored first value, obtaining a second globally accessible value, if the second globally accessible value corresponds to a stored second value, obtaining device characteristics data from a relatively fast memory, if the second globally accessible value does not correspond to the stored second value, obtaining device characteristics data from a relatively slow memory and updating the relatively fast memory, the stored first value, and the stored second value. The globally accessible first value may include device I/O information. The globally accessible values may be stored in global memory that is accessible to a plurality of processors.

Abstract: Queued lock services for managing a shared resource in a data processing system include a cooperative lock override procedure. On detecting a protocol failure by another processor, the detecting processor confirms that the failing processor is the lockholder and passes the lock to the next requestor in the queue.

Abstract: A hierarchical, probability-based look-up method and apparatus for selection of an operation for job generation. Bitmaps are set based on the priority class of pending operation requests. The bitmap values are used to select a priority class and an operation for the selected priority class in a two-step, probability-based table look-up.

Abstract: Described are techniques for performing multi-sequential I/O operations in connection with data requests involving a data storage device. An single data request may involve more than a one portion of data associated with a single job record, such as a single request may involve more than a single track of data of a logical device. A single job record corresponds to a single track. A data structure arrangement is disclosed that includes multiple job records corresponding to the single data request involving more than a single track of data. The multiple job records for a single data request are connected together in a data structure arrangement that may be used in connection with a single read operation involving more than a single track of data.

Abstract: Storing data in a cache memory of a storage device includes providing access to a first segment of the cache memory on behalf of a first group of external host systems coupled to the storage device and providing access to a second segment of the cache memory on behalf of a second group of external host systems coupled to the storage device, where at least a portion of the second segment of the cache memory is not part of the first segment of the cache memory. In some embodiments, no portion of the second segment of the cache memory is part of the first segment. Storing data in a cache memory of a storage device may also include providing a first data structure in the first segment of the cache memory and providing a second data structure in the second segment of the cache memory, where accessing the first segment includes accessing the first data structure and accessing the second segment includes accessing the second data structure. The data structures may be doubly linked ring lists of blocks of data.

Abstract: A lock for managing shared resources in a data processing system enables a requesting processor, in a signal atomic transaction, to validate the main lock data structure, request a lock, take the lock and establish a lock mode if successful, or establish its place in a queue of requesters for subsequent locks on the shared resource if unsuccessful.

Abstract: Determining device characteristics includes obtaining a first globally accessible value, if the first globally accessible value corresponds to a stored first value, obtaining device characteristics data from a relatively fast memory, if the first globally accessible value does not correspond to the stored first value, obtaining a second globally accessible value, if the second globally accessible value corresponds to a stored second value, obtaining device characteristics data from a relatively fast memory, if the second globally accessible value does not correspond to the stored second value, obtaining device characteristics data from a relatively slow memory and updating the relatively fast memory, the stored first value, and the stored second value. The globally accessible first value may include device I/O information. The globally accessible values may be stored in global memory that is accessible to a plurality of processors.

Abstract: A queued, multimodal, fault-tolerant lock mechanism for managing shared resources in a data processing system is provided. Lock override procedures are selectively associated with certain lock modes.

Abstract: A scheduler for selecting a logical volume for job generation based on the loading of physical resources in a data storage system. The scheduler determines a job workload for each of the physical resources, selects physical resources based on the job workload and selects a logical volume supported by the selected physical resources in a balanced manner.

Abstract: Accessing stored data includes providing a virtual storage area having a table of pointers that point to sections of at least two other storage areas, where the virtual storage area contains no sections of data, in response to a request for accessing data of the virtual storage area, determining which particular one of the other storage areas contain the data, and accessing the data on the particular one of the other storage areas using the table of pointers. Accessing stored data may also include associating a first one of the other storage areas with the virtual storage area, where the virtual area device represents a copy of data of the first one of the other storage areas. Accessing stored data may also include causing all of the pointers of the table to initially point to sections of the first one of the other storage areas when the virtual storage area is initially associated with the first one of the other storage areas. The storage areas may be storage devices. The sections may be tracks.

Abstract: A queued, multimodal, self-validating lock mechanism selectively associates supplemental validation procedures with certain lock modes. Only those lock modes which heavily drain system resources are extensively validated.

Abstract: Storing data in a cache memory includes providing a first mechanism for allowing exclusive access to a first portion of the cache memory and providing a second mechanism for allowing exclusive access to a second portion of the cache memory, where exclusive access to the first portion is independent of exclusive access to the second portion. The first and second mechanisms may be software locks. Allowing exclusive access may also include providing a first data structure in the first portion of the cache memory and providing a second data structure in the second portion of the cache memory, where accessing the first portion includes accessing the first data structure and accessing the second portion includes accessing the second data structure. The data structures may doubly linked ring lists of blocks of data and the blocks may correspond to a track on a disk drive. The technique described herein may be generalized to any number of portions.

Abstract: A queued lock prioritizes access to a shared resource in a distributed system. Each unsuccessful requestor adaptively delays its next poll for the lock by a period determined as a function of its priority in the lock request queue and the average duration of a significant processor operation involving the resource.