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Buffered Writing in a Peripheral Storage Hierarchy

IP.com Disclosure Number: IPCOM000050192D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Duke, AH: AUTHOR [+4]

Abstract

The host supplies data to be recorded retentively on a direct-access storage device (DASD) via a volatile cache. For data integrity purposes, normal operations require that each record be retentively stored before a device end (DE) is supplied to the host for ensuring data integrity. The host in selective chains can supply a buffered write (BW) control attribute signifying that any succession of write commands can be stored in the cache with intermediate device ends signifying only receipt of the data, and that the last device end in the succession of writes will signify that all proceeding writes in such succession are retentively stored in the storage hierarchy.

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Buffered Writing in a Peripheral Storage Hierarchy

The host supplies data to be recorded retentively on a direct-access storage device (DASD) via a volatile cache. For data integrity purposes, normal operations require that each record be retentively stored before a device end (DE) is supplied to the host for ensuring data integrity. The host in selective chains can supply a buffered write (BW) control attribute signifying that any succession of write commands can be stored in the cache with intermediate device ends signifying only receipt of the data, and that the last device end in the succession of writes will signify that all proceeding writes in such succession are retentively stored in the storage hierarchy. A succession of writes can be a complete chain of write commands, a series of write commands within a chain having the BW attribute, such succession having no intervening control commands, cache misses, a change in the write command, a read command, track switching or other special conditions. In other words, buffered writing is limited to a succession of write commands of the same type within a given cylinder of tracks of the DASD.

The drawing shows a succession of write commands A-D in which all writes result in a cache hit (space is allocated in the cache to receive the data from the host without an intervening allocation step). Upon the completion of writing A (WRA), the location of the data is only in the cache (C), with a response of device end (DE) being sent to the host. The same response is sent for data elements B and C, wherein the data is only stored in the volatile cache. Upon completion of the fourth command (WRD), the data is only stored in the cache (C) while there is no response of device end to the host. The other conditions will be detected upon receipt of the next command. This particular set of circumstances will be described later. Subsequent to WRD being executed, at the end of the chain and before DE is sent to the host, the storage hierarchy, independently of and disconnected from the host, transfers A through D from cache (C) to DASD (D). Upon completion of each of the data transfers, the data resides both in the cache and DASD. Upon completion of the last offline data transfer to DASD, a device end (DE) is sent to the host s...