SSD Controller Spare Area Management for Read-Only Failure

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Solution Overview

Problem

Solid State Drives (SSDs) face issues with bad areas in NAND flash memory, leading to reduced storage capacity and eventual failure when bad areas exceed spare areas, causing the SSD to enter a read-only mode, where further writing is not possible.

Innovation Solution

Implementing a controller with a write control unit and area management unit that manages spare areas, ensuring writing continues until no valid data is stored in spare areas, and transmitting errors to the host when spare areas are depleted, thereby prolonging the SSD's usability and allowing it to return to a writable state.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If spare areas are used to compensate for bad areas, then storage capacity is maintained, but the SSD enters read-only mode when spare areas are depleted

Engineering Contradiction:

ImproveSSD usabilityVSAvoidwriting capability

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent segments the storage space into multiple regions including spare areas and user data areas. By dividing the storage space and managing different segments independently, the system can relocate data between segments to preserve writing capability even when some areas become bad, thereby maintaining both reliability and productivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements dynamic management of storage areas where the controller can dynamically allocate and relocate data between different storage regions. This dynamic approach allows the system to adapt to bad areas by moving data to healthy regions, preventing the SSD from entering read-only mode and maintaining continuous writing capability.

Inventive Principle:

Principle #15Dynamics

2Reliability

If bad areas are isolated and managed, then data integrity is protected, but storage capacity is reduced

Engineering Contradiction:

Improvedata integrityVSAvoidstorage capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent implements a mechanism where storage areas are temporarily marked as bad and isolated to protect data integrity, but can be recovered and reused after verification. This allows the system to maintain data integrity by isolating problematic areas while recovering and making them available for storage again, thus preserving storage capacity.

Inventive Principle:

Principle #34Discarding and recovering

3Reliability

If spare areas are reserved for bad area compensation, then manufacturing defects are covered, but user storage space is reduced

Engineering Contradiction:

Improvedefect coverageVSAvoiduser storage space

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent implements dynamic management of spare areas where the controller can dynamically allocate spare space to cover bad areas as needed, rather than permanently reserving fixed spare space. This dynamic allocation allows the system to maintain defect coverage while maximizing user storage space by only using spare areas when actually needed for bad area compensation.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS9785384B2Semiconductor storage device and method for controlling nonvolatile semiconductor memory

Publication Date: 2017.10.10 KIOXIA CORP

AI summary

According to embodiments, a controller comprises a write control unit that performs writing in a nonvolatile semiconductor memory, and an area management unit that causes the write control unit to perform write processing until a spare area not storing valid data is not present in the nonvolatile semiconductor memory, and transmits an error to a host when the spare area is not present.