📖 ~1 min read
Table of contents
Symptom & Impact
RAID array enters degraded state, reducing redundancy and increasing risk during additional failures.
Environment & Reproduction
Common after disk errors, cable instability, or replacement drives with mismatched partition geometry.
Root Cause Analysis
A member device is marked faulty or cannot be re-added due to metadata mismatch.
Quick Triage
Review /proc/mdstat and smartctl before forcing assembly or starting rebuild operations.
Step-by-Step Diagnosis
Validate member superblocks, failed disk health, and mdadm event counters for split-brain risk.
Solution – Primary Fix
Replace faulty drive, replicate partition table, re-add member, and monitor rebuild to completion.
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Solution – Alternative Approaches
Fail over to replicated storage or backups if array consistency is uncertain.
Verification & Acceptance Criteria
Array reports clean state with all expected devices active and synced.
Rollback Plan
Stop rebuild and restore from backup if data mismatch appears during parity resync.
Prevention & Hardening
Schedule SMART checks, mdadm monitor alerts, and periodic array scrub operations.
Related Errors & Cross-Refs
mdadm: device faulty, array degraded, and recovery stalled indicators.
Related tutorial: View the step-by-step tutorial for Debian 12.
View all Debian 12 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Debian RAID and mdadm recovery guidelines for production Linux systems.
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