Automated RAID Double Failure Recovery via Slice Migration
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Solution Overview
Problem
RAID double failures in storage systems render data stored in back-end tracks vulnerable to loss, as existing technologies cannot effectively protect and recover data when multiple failures occur within a RAID protection group, leading to potential data loss if subsequent failures happen.
Innovation Solution
The solution involves detecting a RAID double failure and adding a new slice to the RAID protection group, moving front-end tracks from good back-end tracks of the failed slice to the new slice, making write-pending tracks write to the new slice, and using local or remote backups to restore data, ensuring data integrity and minimizing further loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a new slice is added to the RAID protection group to recover from double failure, then data protection capability is improved, but device complexity increases
Solution Approach 1:
The RAID protection group is divided into multiple slices, allowing the system to isolate and manage failures at the slice level. When a double failure occurs in one slice, only that slice needs to be recovered by creating a new slice, rather than reconstructing the entire RAID group, thus improving data protection while managing complexity through modular organization.
Solution Approach 2:
The system proactively detects double failures and automatically initiates recovery by adding new slices before data loss occurs. The front-end tracks are moved to new back-end tracks in advance, and write-pending operations are handled preemptively, ensuring data protection capability is restored before any actual data loss can happen.
2Reliability
If front-end tracks are moved to new back-end tracks to recover data, then data integrity is improved, but loss of time increases
Solution Approach 1:
The system performs preliminary detection of double failures and automatically initiates the slice recovery process before data loss occurs. By proactively moving front-end tracks to new back-end tracks and handling write-pending operations in advance, the system minimizes the actual data loss time while ensuring data integrity is restored.
Solution Approach 2:
The RAID system automatically detects double failures, creates new slices, moves data tracks, and manages write-pending operations without external intervention. This self-service capability reduces recovery time by eliminating manual intervention delays while maintaining data integrity through automated error correction procedures.
3Reliability
If write-pending tracks are restored from local or remote backups, then data protection is improved, but loss of substance increases
Solution Approach 1:
The system uses backup storage as an intermediary resource to restore write-pending tracks when double failures occur. By selectively restoring only the affected front-end tracks from local or remote backups rather than entire data sets, the system improves data protection while minimizing the consumption of backup storage resources through targeted recovery operations.
Data Source
AI summary
Occurrence of a RAID double failure in a slice of a RAID protection group (failed slice) renders data stored in the back-end tracks of the failed slice vulnerable to loss. When a RAID double failure is detected, a new slice is added to the RAID protection group. Front-end tracks that map to the good back-end tracks of the failed slice are moved from the back-end tracks of the failed slice to the back-end tracks of the newly added slice. Any front-end tracks that mapped to the bad back-end tracks of the failed slice are made to be write pending and written to corresponding back-end tracks of the newly added slice. Front-end tracks that map to the bad back-end tracks may be made to be write-pending in connection with a host write operation, by reading the front-end tracks from a local backup, or from a remote backup location.