📖 ~1 min read
Table of contents
Symptom & Impact
RAID array enters degraded state, reducing redundancy and increasing data loss risk.
Environment & Reproduction
Common after disk faults, cable instability, or replacement drives with mismatched layout.
Root Cause Analysis
A member is marked faulty or cannot rejoin due to metadata mismatch.
Quick Triage
Inspect /proc/mdstat and SMART status before forcing assembly or rebuild.
Step-by-Step Diagnosis
Validate superblocks, device health, and mdadm event counters for consistency risk.
Solution – Primary Fix
Replace faulty drive, clone partition table, re-add member, and monitor rebuild completion.
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Solution – Alternative Approaches
Fail over to replicated storage or backup restore if array consistency is uncertain.
Verification & Acceptance Criteria
Array reaches clean state with all expected devices active and synced.
Rollback Plan
Stop rebuild and restore from backup if parity resync reveals data mismatch.
Prevention & Hardening
Schedule SMART checks, mdadm monitoring alerts, and periodic scrub operations.
Related Errors & Cross-Refs
mdadm device faulty, degraded array state, and stalled recovery indicators.
Related tutorial: View the step-by-step tutorial for Debian 9.
View all Debian 9 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Debian RAID and mdadm recovery guidance for production Linux systems.
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