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Method for Determining the Physical Location of an Unreadable Logical Sector

IP.com Disclosure Number: IPCOM000047148D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 4 page(s) / 73K

Publishing Venue

IBM

Related People

Boscove, JA: AUTHOR

Abstract

This method allows an alternate sector assignment to be completed when the logical sector involved is defective and unreadable for the case of a multiple platter magnetic disk file wherein, for each cylinder, consecutive logical sectors are read or written on an angle down the length of the cylinder. This non-conventional sector assignment format is described in [*]. When assigning an alternate sector for a magnetic disk file, it is necessary to obtain the physical location of the defective section in question. The physical location is needed to write the sector ID with a "defective sector" bit in the flag field of the sector ID. The "Write sector ID" operation requires a physical sector location as an address parameter to locate the sector.

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Method for Determining the Physical Location of an Unreadable Logical Sector

This method allows an alternate sector assignment to be completed when the logical sector involved is defective and unreadable for the case of a multiple platter magnetic disk file wherein, for each cylinder, consecutive logical sectors are read or written on an angle down the length of the cylinder. This non-conventional sector assignment format is described in [*]. When assigning an alternate sector for a magnetic disk file, it is necessary to obtain the physical location of the defective section in question. The physical location is needed to write the sector ID with a "defective sector" bit in the flag field of the sector ID.

The "Write sector ID" operation requires a physical sector location as an address parameter to locate the sector. Due to the unique method of formatting and assigning alternate sectors with the angular sector format, the user does not know the physical location of a defective logical record. In fact, the user does not know the logical sector number of a data record. Normal references for data records are expressed as a relative block address (RBA). An RBA is an integer value identifying the position of a data record relative to the beginning of the disk file. Every data record on the disk file has its own unique RBA. The RBA is passed to the disk controller as an address parameter to read or write a data record.

The disk controller converts the RBA to a cylinder number and a logical sector number and then performs the read or write operation.

In order to obtain the physical location of a data record, the user must issue a "Read Scan ID" command supplying an RBA as an address parameter. The physical location is part of the sector ID. The disk controller converts the RBA to a cylinder number and a logical sector number, seeks to the proper cylinder, and searches for the cylinder and logical sector number which is also in the sector ID. If the search is successful, the sector ID is returned to the user. The user then extracts the physical location from the ID and proceeds to assign an alternate sector. If the search is unsuccessful, due to the ID in question being unreadable (defective), the controller is unable to return the sector ID to the user. Therein lies the problem. The problem is solved by using the following procedure in either a system program or in the disk controller's microcode. Adherence to the angular sector assignment specifications in formatting and assigning alternate sectors is necessary for the program to accomplish its task. The program calculates 21 predictable physical sector locations based on the logical input number. Up to 21 physical sectors are read looking for an unreadable ID. After the unreadable ID is detected, further analysis is made by examining the data in the second data field to determine that the proper physical sector number has been calculated. This program is shown in the flow chart, and th...