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Improving Direct Access Storage Device Reclaim

IP.com Disclosure Number: IPCOM000040126D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 65K

Publishing Venue

IBM

Related People

Crowley, TR: AUTHOR [+2]

Abstract

The use of a displacement field in the alternate sector ID of a disk data storage device permits a reclaim program to more efficiently compute the Physical address of the primary sector associated with the alternate sector to reclaim. A direct access storage device (DASD) unit consists of multiple cylinders. Each cylinder contains multiple heads which access multiple sectors. Each sector consists of an ID field and a data field. The format of the ID field is as follows: (Image Omitted) BYTE Bit Field ---- --- ----- 0 0-2 Displacement amount 0 3 Reassigned (1=yes) 0 4 Alternate (1=yes) 0 5-6 Defect flags 0 7 Reserved 1-3 Logical address (Head, cylinder, sector).

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Improving Direct Access Storage Device Reclaim

The use of a displacement field in the alternate sector ID of a disk data storage device permits a reclaim program to more efficiently compute the Physical address of the primary sector associated with the alternate sector to reclaim. A direct access storage device (DASD) unit consists of multiple cylinders. Each cylinder contains multiple heads which access multiple sectors. Each sector consists of an ID field and a data field. The format of the ID field is as follows:

(Image Omitted)

BYTE

Bit Field

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

0 0-2 Displacement amount

0 3 Reassigned (1=yes)

0 4 Alternate (1=yes)

0 5-6 Defect flags

0 7 Reserved

1-3 Logical address (Head, cylinder, sector).

4-6 Physical address (Head, cylinder, sector).

Identifies the actual location of the sector

on the disk unit.

7 Zero There are 'N' sectors on each of the heads on a cylinder. 'N-1' sectors are available for user data.

These sectors are referred to as primary sectors. Sector 'N' is referred to as an alternate location. In the manufacturing process, the ID of every sector initially has the logical address equated to the Physical address. Manufacturing surface-analysis tests determine which sectors do not meet acceptable criteria for data error conditions, and do the following (see Fig. 1): 1. The failing sector is marked as 'defective' (byte 0 bits 5-6

of the ID are set). 2.The sector field in the Logical address is set equal to FF. 3.All subsequent sectors on that head are reassigned so that

the defective sector will now occupy the space currently

occupied by the next sequential sector. Sector 'N-1' will

occupy sector location 'N'. 4.The displacement field (byte 0, bit 0-2 of the ID) of each

reassigned sector is incremented by 1. Any subsequent sector error found on the...