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METHOD FOR FILTERING UPDATE WRITE CCWs IN ECKD ARCHITECTURE

IP.com Disclosure Number: IPCOM000034410D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Bello, KA: AUTHOR [+5]

Abstract

Extended Count Key Data (ECKD) architecture requires that when performing update writes to a DASD, a transfer length check is performed. This is to insure data integrity. The length of key and data fields must equal the number of bytes being transferred from the channel. Two types of ECKD environments chain update write CCWs (Channel Control Words): -- Update Write -- Write Track Only update write CCWs require transfer length checking. Also transfer length checking is not to be done while the device is performing a Find Operation. A Find means the device process is searching for the field(s) of interest of the channel process. The problem is filtering the proper command and determining the correct environment. This was accomplished by performing a look-ahead on the next command to be processed by the device.

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METHOD FOR FILTERING UPDATE WRITE CCWs IN ECKD ARCHITECTURE

Extended Count Key Data (ECKD) architecture requires that when performing update writes to a DASD, a transfer length check is performed. This is to insure data integrity. The length of key and data fields must equal the number of bytes being transferred from the channel. Two types of ECKD environments chain update write CCWs (Channel Control Words): -- Update Write -- Write Track Only update write CCWs require transfer length checking. Also transfer length checking is not to be done while the device is performing a Find Operation. A Find means the device process is searching for the field(s) of interest of the channel process. The problem is filtering the proper command and determining the correct environment. This was accomplished by performing a look-ahead on the next command to be processed by the device. The device process actually looked at the next command before the channel process issued it. The past implementation is no longer suitable, therefore, a new filter was devised. This new filter mechanism is not required to know upcoming operations. It takes advantage of the ECKD architecture. The necessary information to implement this filter is:
1. The operation the device is currently performing 2. The environment/domain set up by the LOCATE RECORD CCW The following chart illustrates the only conditions needed to determine whether or not transfer length checking must be performed. DEVICE OPERATION F...