Browse Prior Art Database

DASD Update Processing

IP.com Disclosure Number: IPCOM000039021D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Iskiyan, J: AUTHOR [+5]

Abstract

When non-retentive data is written, ending status is presented to the channel when the data has been transferred from the channel to the cache. The non-retentive data is written to the disk device (DASD) when the non-retentive data becomes Least Recently Used (LRU). If the data never becomes Least Recently Used (e.g., data is frequently accessed), the data will never be written to the DASD. The user needs the ability to ensure that the data is on the DASD without causing a performance impact. With the Schedule DASD Update (SDU) option, all non-retentive data for the device is scheduled for destage (Write to DASD) as a background operation. Channel commands to the specific device are still allowed which enable the performance level to be maintained.

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DASD Update Processing

When non-retentive data is written, ending status is presented to the channel when the data has been transferred from the channel to the cache. The non- retentive data is written to the disk device (DASD) when the non-retentive data becomes Least Recently Used (LRU). If the data never becomes Least Recently Used (e.g., data is frequently accessed), the data will never be written to the DASD. The user needs the ability to ensure that the data is on the DASD without causing a performance impact. With the Schedule DASD Update (SDU) option, all non-retentive data for the device is scheduled for destage (Write to DASD) as a background operation. Channel commands to the specific device are still allowed which enable the performance level to be maintained. The user can determine when all non-retentive data has been written to DASD by reading an indicator maintained by the microcode using the Sense Subsystem Status channel command. The SDU function will be dispatched when no higher priority work is to be done. When the SDU function is dispatched the Modified Bit Map (MBM) contained in the device subsystem storage is read until a track is found that contains modified data. When found, an internal command chain to locate and write all modified records on the same track is built and added to a dispatch queue. The write operation will be dispatched, and all modified records on the track will be written to the device. After the records have been written...