SSD Mirroring Control for Asymmetric Wear Distribution

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Solution Overview

Problem

Mirroring devices using two SSDs face challenges in improving fault tolerance without prematurely exhausting one SSD, as they reach their rewrite limits simultaneously due to repeated data writing, and existing solutions like dummy data storage can lead to early SSD failure.

Innovation Solution

A mirroring device with a control mechanism that acquires and compares the remaining writable amounts of two SSDs, adjusting data storage modes to ensure a predetermined difference is maintained, thereby preventing simultaneous SSD exhaustion and improving fault tolerance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If dummy data is repeatedly stored in only one of the SSDs to create a difference in rewrite times, then the two SSDs can reach their lifetimes at different times, but the one SSD accumulates excessive dummy data and reaches lifetime early

Engineering Contradiction:

Improvefault toleranceVSAvoidSSD lifetime

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The invention segments the dummy data storage task across multiple SSDs rather than concentrating it in one SSD. By distributing the accumulation of dummy data across both SSDs in the mirroring device, each SSD bears a portion of the rewrite load, preventing any single SSD from reaching its lifetime limit prematurely while still maintaining the necessary difference in rewrite times to achieve fault tolerance.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the same data is written repeatedly in two SSDs to improve fault tolerance, then the fault tolerance is improved, but the two SSDs reach their lifetimes at almost the same time

Engineering Contradiction:

Improvefault toleranceVSAvoidSSD simultaneous failure risk

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The invention introduces asymmetry in the data writing pattern between the two SSDs. Instead of writing identical data to both SSDs simultaneously, the system writes different data to each SSD, creating a deliberate difference in their rewrite counts. This asymmetric approach ensures that the SSDs wear at different rates, separating their failure times and improving overall system reliability.

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentUS9779001B2Mirroring device, control method thereof, and storage medium that maintain difference in remaining writable amounts of data

Publication Date: 2017.10.03 CANON KK

AI summary

A mirroring device that can improve, even when two storage devices to which an upper limit is set for the number of rewrites of data are used, the fault tolerance of the mirroring device while preventing one of the storage devices from reaching the lifetime thereof early. A mirroring device comprises two storage devices to which an upper limit is set for the number of rewrites of data. Remaining writable amounts of the data in the storage devices are acquired respectively from total amounts of the data written in the respective storage devices. When it is determined that a difference between the respective acquired remaining writable amounts is less than a predetermined value, the respective storage devices are controlled such that the difference becomes equal to or more than the predetermined value.