Hybrid Drive Dual ECC Storage for NVSM Capacity and Recovery

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Solution Overview

Problem

Hybrid drives face limitations in storage capacity and performance due to the overhead of error correction codes (ECC) in non-volatile semiconductor memory (NVSM), which reduces the reliability and efficiency of data storage.

Innovation Solution

Implementing a dual ECC system where a first set of ECC symbols is used for routine error correction and a second, more extensive set is generated for recovery, with the latter being cached in volatile memory to minimize disk access latency and stored on disk for critical errors, using generator polynomials like Reed-Solomon codes to ensure data integrity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If extended ECC symbols are written to NVSM for every data sector, then data recovery capability is improved, but storage capacity is reduced due to overhead

Engineering Contradiction:

Improvedata recovery capabilityVSAvoidstorage capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent divides ECC symbols into two segments: first ECC symbols stored in NVSM with data sectors, and second extended ECC symbols stored on the disk. This segmentation allows the system to achieve enhanced error correction capability while avoiding the storage capacity penalty of storing all extended ECC symbols in NVSM, as the disk provides abundant space for the second set of symbols.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent moves the storage of extended ECC symbols from the NVSM dimension to the disk dimension. By leveraging the disk's large storage capacity, the system can store comprehensive extended ECC symbols without consuming NVSM capacity, thus maintaining user data capacity while achieving improved data recovery capability.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If extended ECC symbols are stored in NVSM, then data recovery is improved, but access latency increases due to NVSM constraints

Engineering Contradiction:

Improvedata recoveryVSAvoidaccess latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent extracts the storage of extended ECC symbols from the NVSM and places them on the disk. This extraction eliminates the constraint of NVSM capacity and access patterns, allowing the system to store comprehensive extended ECC symbols without impacting NVSM performance or access latency.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces the disk as an intermediary storage medium for extended ECC symbols. The disk acts as a mediator that provides abundant storage space for comprehensive ECC symbols without imposing NVSM's access latency constraints, thus enabling improved data recovery without performance degradation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If more ECC symbols are generated for each data sector, then error correction capability is improved, but write amplification of NVSM increases

Engineering Contradiction:

Improveerror correction capabilityVSAvoidwrite amplification

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The patent merges the storage of first ECC symbols in NVSM with second extended ECC symbols on the disk. This combination allows the system to provide comprehensive error correction capability while distributing the storage burden, thereby reducing the write amplification impact on NVSM compared to storing all ECC symbols in NVSM alone.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS8683295B1Hybrid drive writing extended error correction code symbols to disk for data sectors stored in non-volatile semiconductor memory

Publication Date: 2014.03.25 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A hybrid drive is disclosed comprising a head actuated over a disk, and a non-volatile semiconductor memory (NVSM). A write command is received from a host, the write command comprising data. First and second error correction code (ECC) symbols are generated over the data, wherein the second ECC symbols are different than the first ECC symbols. The data and first ECC symbols are written to the NVSM, and the second ECC symbols are written to the disk.