Browse Prior Art Database

Data Recovery in a File When File Index Has I/O Errors

IP.com Disclosure Number: IPCOM000046955D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Yu, MK: AUTHOR [+3]

Abstract

When a sequential access method recovery routine finds an input/output error in a diskette table of contents, it will delete the index block that is in error. The data referenced by the index block will then become completely inaccessible. However, when the file recovery method scans the data, it is necessary for the file recovery method to know where the data is lost. The file recovery method also needs to post a message to tell the user where the data is lost. It is therefore necessary for the file recovery method to be able to find where the index blocks are deleted. With reference to the figure, when the sequential access method deletes any index blocks, a marker bit in the previous index block is set to indicate that the next block is deleted.

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Data Recovery in a File When File Index Has I/O Errors

When a sequential access method recovery routine finds an input/output error in a diskette table of contents, it will delete the index block that is in error. The data referenced by the index block will then become completely inaccessible. However, when the file recovery method scans the data, it is necessary for the file recovery method to know where the data is lost. The file recovery method also needs to post a message to tell the user where the data is lost. It is therefore necessary for the file recovery method to be able to find where the index blocks are deleted. With reference to the figure, when the sequential access method deletes any index blocks, a marker bit in the previous index block is set to indicate that the next block is deleted. When the file recovery method is scanning the file, the marker bit is checked to see if any deletion has occurred. When such a marker is found, the file recovery method can delete partial records before the lost data, delete partial records after the lost data, and post a message, "Data lost after Record ID . This procedure permits an inexpensive way of communicating between the sequential access method and the file recovery method, allowing the data stream to be cleared up and an appropriate message to be posted.

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