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Method for Allocating Spare Sectors After SAT

IP.com Disclosure Number: IPCOM000060999D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 28K

Publishing Venue

IBM

Related People

Styczinski, DA: AUTHOR

Abstract

A surface-analysis test (SAT) at time of manufacture of disk drives determines which sectors are defective. In this method, spare sectors are allocated uniformly so that subsequently grown defective sectors will be near a spare and the push-down will be short. As nonuniformities in spares develop during the life of a disk drive, a utility program can be run to redistribute the spares. Allocating spares uniformly is illustrated by the following example. The number of sectors per track in the example is much less than for a real file. Example specifications: . 14 sectors per track . 4 tracks per cylinder . 2 defects per cylinder (average SAT defect rate) . 1 spare per track after SAT . 7 maximum length of defect list. Information derived from the specifications and assumptions: . 56 physical sectors per cylinder .

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Method for Allocating Spare Sectors After SAT

A surface-analysis test (SAT) at time of manufacture of disk drives determines which sectors are defective. In this method, spare sectors are allocated uniformly so that subsequently grown defective sectors will be near a spare and the push-down will be short. As nonuniformities in spares develop during the life of a disk drive, a utility program can be run to redistribute the spares. Allocating spares uniformly is illustrated by the following example. The number of sectors per track in the example is much less than for a real file. Example specifications:
. 14 sectors per track . 4 tracks per cylinder . 2 defects per cylinder (average SAT defect rate) . 1 spare per track after SAT . 7 maximum length of defect list. Information derived from the specifications and assumptions: . 56 physical sectors per cylinder . 6 unused sectors per cylinder (average) defects and spares . 50 sectors per logical cylinder . 13 logical sectors on each logical track (0, 1, 2) . 11 logical sectors on logical track 3.

(Image Omitted)

The cylinder diagramed above illustrates the configuration when there are no defects on the cylinder and no sectors relocated onto it from the previous cylinder. Most of the cylinders on a file will be like this. S represents the unused spare sectors. The first sector is known as a spare by the coincidence of two conditions. 1. The displacement 1 is added to 1, the first physical sector number (PSN), to get to the first logical sector. 2. The displacement of the previous track plus the number of defects on the previous track (0) plus the logical length of the previous track (13 or 11) is less than the physical length of the previous track, so the potential spare identified by condition 1 is not loaned to the previous track,
i.e., it is available. The track on which a sector would normally reside must be read in order to determine that it has been moved to the next track. The following code is used in the examples: " " = data not relocated off track S = spare U = used on track, was a spare before SAT D = defect found during SAT L = loaned to previous track during SAT G = grown defect (during use in the field) R = relocated data at end of push-down (pull-up). The used data sectors are always maintained in sequence. After growing defects, the cylinder diagrammed in the example appears as:

(Image Omitted)

Grown defect G1 has caused the use of the spare on track 1 by way of a pull-up relocation. Notice that the displacement has been changed to 0 to reflect that the first sector on logical track 1 is PSN 1. Every sector on track 1 has been rewritten. Grown defect G2 has caused the use of the spare on track 3 by way of a push-down relocation. All of track 2 has been rewritten, but only PSN 1 of track 3 to accomplish the relocation. This e...