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Using DASD Scan Results to Improve DASD Save Operations

IP.com Disclosure Number: IPCOM000039983D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Crowley, TR: AUTHOR [+2]

Abstract

Verifying the readability of DASD (direct access storage device) sectors before attempting to save DASD data improves the performance of a Save operation. The Save operation does not waste time running error recovery procedures on sectors which a Scan operation has already identified as containing uncorrectable errors. (Image Omitted) A procedure (hereafter referred to as a Scan operation) executes a 'verify' command on each sector of the DASD unit (Fig. 1). The 'verify' command response data indicates if a sector has an error and the type of the error (correctable or uncorrectable). The 'verify' command does not transfer the DASD data into mainstore, and executes many times faster than a 'read-data' command. The results of the Scan operation are placed in a table (referred to as the Scan-Table).

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Using DASD Scan Results to Improve DASD Save Operations

Verifying the readability of DASD (direct access storage device) sectors before attempting to save DASD data improves the performance of a Save operation. The Save operation does not waste time running error recovery procedures on sectors which a Scan operation has already identified as containing uncorrectable errors.

(Image Omitted)

A procedure (hereafter referred to as a Scan operation) executes a 'verify' command on each sector of the DASD unit (Fig. 1). The 'verify' command response data indicates if a sector has an error and the type of the error (correctable or uncorrectable). The 'verify' command does not transfer the DASD data into mainstore, and executes many times faster than a 'read-data' command. The results of the Scan operation are placed in a table (referred to as the Scan-Table). The format of the Scan-Table is as follows: Byte Contents

---- --------

0-3 Count of entries in the Scan-Table

4-6 Address of 1st Sector with uncorrectable error

7-9 Address of 2nd Sector with uncorrectable error

: :

XXX-YYY Address of 'N'th Sector with uncorrectable error

When an uncorrectable error is found on a sector from a DASD unit belonging to a parity set of sectors, one of which contains parity for the set, a decision point is re-analyzed. The following items are summed: . The amount of time required to complete the Scan

operation

on the remainder of the DASD unit.

. The amount of time required to read the data from every

sector on the DASD unit. For each entry in the Scan-Table,

compute the amount of time needed to read the other DASD

units in the set in order to recreate the data in those

sectors....