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Formatting of Variable Length (CKD) Records on DASD Tracks Having Periodically Occurring Unwritable Segments

IP.com Disclosure Number: IPCOM000051853D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Dishon, Y: AUTHOR [+2]

Abstract

This article relates to a method for minimizing unused available recording lengths when formatting variable length CKD-type records on DASD (direct-access storage device) tracks periodically interrupted as by way of sector servo information. In such circumstances, recording gaps define time intervals between record fields (count, key, and data). During these intervals READ/WRITE operations are suspended. The gaps include a first extent dedicated to time delay and a second extent dedicated to synchronizing the recording channel to a servo drive.

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Formatting of Variable Length (CKD) Records on DASD Tracks Having Periodically Occurring Unwritable Segments

This article relates to a method for minimizing unused available recording lengths when formatting variable length CKD-type records on DASD (direct- access storage device) tracks periodically interrupted as by way of sector servo information. In such circumstances, recording gaps define time intervals between record fields (count, key, and data). During these intervals READ/WRITE operations are suspended. The gaps include a first extent dedicated to time delay and a second extent dedicated to synchronizing the recording channel to a servo drive.

The method steps include bifurcating (splitting) the gaps, if the remaining track sector available for formatting the gaps is less than the gap length. The first extent of the gap occupies much of the available remaining track, and possibly overlaps the servo area. The second extent of the gap coincides in "that case with the synchronizing gap, normally following a servo area. The steps further include recognition of the size of the available remaining sector before formatting the gap, and then managing the format of the two extents of the gap. It is noted that there exists a possibility of the first extent spanning across the servo area and beyond. In this case, the second extent substitutes for the synchronization gap normally following the servo area.

Reference is made to U.S. Patent 3,997,876, in which only the data format recorded on the track, as distinguished from non-data information, is bifurcated upon a defect extent being encountered. The advance in this case is the splitting of fields, in addition to the data field, into two extents, according to their function, overhead time, and synchronization.

Referring now to the figure, gap G is divided into two parts, namely, GA and GB. GA is that part of the gap required for managing the overhead time, while GB is that part of the gap during which the recording electronics synchronized to the next field requirements. Among these requirements is that it must be contiguous to that field.

When formatting a gap, one of the following strategies is pursued:.

A: If the Remaining Sector (RS) (bytes) > = G, then G is formatted on the remaining sector.

B: If the Remaining Sector < G, the gap is split into GA + GB.

One of the following is then done: B1: If the Remaining Sector > GA, GA is formatted on the remaining sector and the remaining bytes (RS-GA) are wasted. (W field.) GB is then formatted following the Servo field, omitting the g1 field.

B2: If the Remaining Sector = GA, then GA is formatted on the Remaining Sector and GB i...