📖 ~1 min read
Table of contents
Symptom & Impact
RAID enters degraded mode, increasing risk of data loss and reduced performance.
Environment & Reproduction
Appears after member disk timeout, UUID mismatch, or delayed device discovery.
Root Cause Analysis
One or more members fail assembly and are marked faulty during boot.
Quick Triage
Run `cat /proc/mdstat` and identify missing or failed members.
Step-by-Step Diagnosis
Validate metadata UUID consistency across members and review assembly messages in journal.
Solution – Primary Fix
Re-add healthy member or replace failed disk, then monitor rebuild to completion.
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Solution – Alternative Approaches
Assemble array manually in rescue mode when auto-assembly fails.
Verification & Acceptance Criteria
Array returns to clean state with all expected members active.
Rollback Plan
Stop risky rebuild attempt and restore from backup if integrity is uncertain.
Prevention & Hardening
Enable mdadm monitoring and proactive disk health alerting.
Related Errors & Cross-Refs
Can coincide with SATA link resets and controller firmware issues.
Related tutorial: View the step-by-step tutorial for debian-10.
View all debian-10 tutorials on the Tutorials Hub →
Browse all common problems & solutions on the Tutorials Hub.
References & Further Reading
Debian mdadm administration and recovery documentation.
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