Disk Drive Guard Bands for Shingled Track Zone Boundaries

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Solution Overview

Problem

Existing disk drive formats face issues with data track overlapping and inter-track interference during shingled writing, where a previously written data track is partially overwritten twice, potentially rendering it unrecoverable, especially when writing in opposite directions across zones.

Innovation Solution

The implementation of guard bands and pivot points on disk surfaces to prevent data track overlapping, where guard bands comprise unused tracks and pivot points define the boundary for reversing writing directions, reducing inter-track interference and ensuring data track recoverability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If data tracks are written in a shingled manner to increase disk capacity, then disk capacity is improved, but data track overlapping and inter-track interference occur causing tracks to become unrecoverable

Engineering Contradiction:

Improvedisk capacityVSAvoiddata track recoverability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The disk surface is segmented into zones with different data rates, and guard bands are inserted between zones to prevent overlapping. This segmentation allows shingled writing within zones while maintaining track recoverability through the protective guard band boundaries.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Guard bands act as intermediary regions between data tracks written in opposite directions. These unused tracks serve as buffers that prevent inter-track interference and ensure that previously written tracks are not overwritten, thereby maintaining data recoverability while enabling high-density shingled writing.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the data rate is increased toward outer diameter tracks to achieve constant linear bit density, then data rate is improved, but data track overlapping occurs when writing in opposite directions

Engineering Contradiction:

Improvedata rateVSAvoiddata track non-overlapping

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

Different data rates are applied to different zones of the disk surface, with inner diameter zones using lower data rates and outer diameter zones using higher data rates. This local quality adjustment ensures constant linear bit density across the radius while preventing track overlapping through strategically placed guard bands at zone boundaries.

Inventive Principle:

Principle #3Local quality

3Reliability

If guard bands are defined between zones to prevent track overlapping, then data track recoverability is improved, but disk capacity is reduced due to unused tracks

Engineering Contradiction:

Improvedata track recoverabilityVSAvoiddisk capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

Guard bands are applied selectively only at zone boundaries where direction reversals occur, rather than across the entire disk surface. This partial application maintains data recoverability at critical points while minimizing the impact on overall disk capacity.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS8699185B1Disk drive defining guard bands to support zone sequentiality when butterfly writing shingled data tracks

Publication Date: 2014.04.15 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A disk drive is disclosed wherein a plurality of zones are defined on first and second disk surfaces, wherein each zone comprises a plurality of data tracks. Data is written to the data tracks of a first plurality of the zones on the first and second disk surfaces in an interleaved manner, in a first radial direction, and in a shingled manner. Data is written to the data tracks of a second plurality of the zones on the first and second disk surfaces in an interleaved manner, in a second radial direction opposite the first radial direction, and in a shingled manner. At least one guard band is defined at a boundary between a first zone and a second zone in the second plurality of zones on the first disk surface, wherein the guard band comprises at least one unused data track.