🟠 High   ⏱ 5–30 min  Last verified: 20 May 2026
Affected versions: FreeBSD 15

📖 ~1 min read

Table of contents
  1. Symptom & Impact
  2. Environment & Reproduction
  3. Root Cause Analysis
  4. Quick Triage
  5. Step-by-Step Diagnosis
  6. Solution – Primary Fix
  7. Solution – Alternative Approaches
  8. Verification & Acceptance Criteria
  9. Rollback Plan
  10. Prevention & Hardening
  11. Related Errors & Cross-Refs
  12. References & Further Reading

Symptom & Impact

Array runs without redundancy, increasing risk of full data loss on second failure.

Environment & Reproduction

Common after hot-swap where metadata was not initialized correctly.

gmirror status

Root Cause Analysis

New disk lacks expected partition layout or mirror metadata insertion failed.

Quick Triage

Confirm replacement disk visibility and health before rebuild.

camcontrol devlist && smartctl -a /dev/

Step-by-Step Diagnosis

Compare partition geometry between surviving member and replacement disk.

gpart show  && gpart show
Illustrative mockup for freebsd-15 — gmirror_status_degraded
gmirror reports DEGRADED state — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Replicate partition layout, insert new member, and monitor resync.

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sudo gmirror insert  /dev/
Illustrative mockup for freebsd-15 — gmirror_insert_rebuild
Inserting replacement disk and rebuilding mirror — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Migrate to ZFS mirror if redesign is planned and downtime permits.

Verification & Acceptance Criteria

Mirror returns to COMPLETE and rebuild finishes without read errors.

Rollback Plan

Remove faulty replacement member and continue in degraded mode temporarily.

Prevention & Hardening

Standardize replacement workflow with partition cloning scripts.

Related to mismatched sector sizes and controller mode changes.

Related tutorial: View the step-by-step tutorial for freebsd-15.

View all freebsd-15 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

GEOM mirror maintenance and recovery documentation.

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