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Overlapped Controls in a Storage Hierarchy

IP.com Disclosure Number: IPCOM000045322D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Christian, JH: AUTHOR [+2]

Abstract

A storage hierarchy having a cache and a backing main store, such as a plurality of direct-access storage devices (DASDs), has an asynchronous control for transferring data between the cache and the main store. Asynchronous control provides for data transfer through a chain of commands similar to the I/O chain of commands provided by the host to the storage hierarchy. Performance is enhanced by initializing a data transfer request by a SEEK command, for example, for a DASD or other preparatory steps for establishing a data transfer path. While that path is being established, such as by seeking a head to a cylinder in DASD, the asynchronous control simultaneously builds the chain of commands that will immediately follow the preparatory steps.

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Overlapped Controls in a Storage Hierarchy

A storage hierarchy having a cache and a backing main store, such as a plurality of direct-access storage devices (DASDs), has an asynchronous control for transferring data between the cache and the main store. Asynchronous control provides for data transfer through a chain of commands similar to the I/O chain of commands provided by the host to the storage hierarchy. Performance is enhanced by initializing a data transfer request by a SEEK command, for example, for a DASD or other preparatory steps for establishing a data transfer path. While that path is being established, such as by seeking a head to a cylinder in DASD, the asynchronous control simultaneously builds the chain of commands that will immediately follow the preparatory steps.

The host in operating the storage hierarchy generates one or more access requests. The storage hierarchy examines the cache through a directory (not shown) to determine whether or not space has been allocated in the cache relating to the access requests. If space is allocated, a cache hit occurs; otherwise, a cache miss occurs. For a cache hit, the cache is accessed on behalf of the host without reference to the main store. In some situations, a write access (transfer of data from host to the storage hierarchy) can require automatic allocation of space in cache for receiving the host data. In that case, that cache is accessed to the exclusion of the main store. The main store can be...