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New Strategy for Defect Processing for Fixed-Block Devices

IP.com Disclosure Number: IPCOM000039226D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Menon, MJ: AUTHOR

Abstract

Disclosed is a new strategy for defect processing in fixed-block devices. It is characterized by employing skip locators in the ID field of the fixed-block device. The skip locators include data identifying the number of defects in the various fields that fall within the sections identified by the ID field and a second group of variables which describe the possible defect-free sections in the data area. The second group of identifiers each identify either the length of a defect-free section of the data field or a count of the number of defects between two defect-free sections, if the number of such defects exceeds one. A preferred implementation allowing for up to three defects per block uses seven different pieces of locator information in the ID field, called LL1, LL2, LL3, L1, L2, L3, and L4.

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New Strategy for Defect Processing for Fixed-Block Devices

Disclosed is a new strategy for defect processing in fixed-block devices. It is characterized by employing skip locators in the ID field of the fixed-block device. The skip locators include data identifying the number of defects in the various fields that fall within the sections identified by the ID field and a second group of variables which describe the possible defect-free sections in the data area. The second group of identifiers each identify either the length of a defect-free section of the data field or a count of the number of defects between two defect-free sections, if the number of such defects exceeds one. A preferred implementation allowing for up to three defects per block uses seven different pieces of locator information in the ID field, called LL1, LL2, LL3, L1, L2, L3, and L4. LL1 contains the number of defects in the gap between the ID and the data area. LL2 contains the number of defect-free sections in the data area following the ID field. LL3 contains the number of defects in the gap following the data field, before the next ID field. An example illustrating the LL values is shown in the figure. Each defect requires that a number D bytes be skipped. Occasionally, there may be an area of a track where multiple defects occur, and it is not enough to skip D bytes. In that case, D bytes are skipped for each defect. Thus, it is possible to have multiple defects between two defect-free sections. With no more than three defects per block, each of LL1, LL2 and LL3 only needs to be two bits, for a total of six bits. For simplicity, let these three areas occupy one byte. L1 through L4 describe the four possible defect-free sections in the data area. Each of L1 through L4 either is the length, in two bytes, of a defect-free section of the data field, or it is a count of the number of defects between two defect-free sections, if the number of such defects exceeds one. The example of the figure clarifies the values stored in these fields.

For the 3370, the data area is 512 bytes or 256 two-bytes. Therefore, the length of any defect-free section also cannot exceed 256 two-bytes. Hence, seven bits suffice to represent the length of a defect-free section. Each of L1 throug...