RAID Spare Group Assignment for Sequential Drive Failure Recovery

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Solution Overview

Problem

Existing RAID systems struggle to efficiently manage and recover from multiple sequential drive failures in non-volatile storage systems, leading to potential data loss and inefficiencies in rebuilding protection group members.

Innovation Solution

A method and apparatus that configure non-volatile drives into a matrix representation with sequentially numbered rows and columns, reserve spare groups, and utilize an ordered target and source list to assign spare cells for rebuilding protection group members after drive failures, ensuring all members are on different disks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional RAID systems are used for non-volatile storage, then data storage capacity is maintained, but the system cannot efficiently recover from multiple sequential drive failures

Engineering Contradiction:

Improverecoverability from multiple sequential drive failuresVSAvoidcomplexity of managing spare capacity and rebuilding protection group members

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system segments spare capacity into discrete spare groups, each associated with specific protection groups. This segmentation allows targeted recovery operations where spare cells can be precisely assigned to rebuild members on failed drives, enabling efficient handling of multiple sequential failures without managing the entire spare pool as a single unit.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system performs preliminary actions by pre-configuring spare groups and establishing ordered source and target lists before failures occur. When a drive fails, the rebuilding process can immediately proceed using pre-organized lists of source cells and target spare cells, eliminating the need for complex real-time allocation decisions during failure recovery.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If multiple sequential drive failures occur, then data loss risk increases, but traditional RAID systems lack the mechanism to efficiently rebuild protection group members

Engineering Contradiction:

Improvedata availability during sequential drive failuresVSAvoidrecovery time for rebuilding protection group members

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system creates ordered source lists and target lists in advance, mapping which spare cells should receive data from which source cells on failed drives. This pre-planning enables immediate execution of rebuild operations when failures occur, significantly reducing recovery time compared to systems that must calculate and determine allocation on-the-fly.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the ordered list mechanism as a feedback structure that guides the rebuild process. By maintaining predetermined source and target lists, the system provides a clear feedback path for data reconstruction, ensuring that spare capacity is systematically applied to restore protection group members in a controlled sequence that maintains data availability.

Inventive Principle:

Principle #23Feedback

3Productivity

If spare capacity is not systematically assigned, then resource utilization is inefficient, but ad-hoc assignment complicates recovery from multiple sequential failures

Engineering Contradiction:

Improveefficiency of rebuilding protection group membersVSAvoidcomplexity of spare capacity management

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The system performs preliminary organization by creating ordered source lists and target lists that map spare cells to protection group members before failures occur. This advance preparation transforms complex real-time allocation decisions into simple execution of predetermined assignments, improving rebuild efficiency while maintaining manageable system complexity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the state of spare capacity from an unstructured resource to one organized by ordered lists with specific parameters (source cell identifiers, target spare cell identifiers, protection group associations). This parameterization of spare capacity management enables systematic and efficient allocation during recovery operations.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250238337A1Raid configuration and spare capacity assignment with recoverability from multiple sequential failures

Publication Date: 2025.07.24 DELL PROD LP

AI summary

Sequentially ordered groups of same-size cells are distributed in a drive array representative matrix as group number=((row number-1)+ (column number-1)) modulo (N), where N is the total number of drives. A plurality of the groups are reserved as spare groups. Responsive to a drive failure, one of the spare groups is selected, an ordered target list of spare cells is created, an ordered source list of cells containing protection group members on the failed drive is created, and the spare cells are assigned to the cells containing protection group members on the failed drive, where the protection group members are rebuilt. The target list starts at the spare cell having the minimum drive index that is greater than the failed drive index. The source list is ordered by either sequential cell indices or alphabetically by group-representing letters.