FreeBSD 12 – ZFS pool degraded after drive errors – Fix & Prevention

📖 ~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

Pool status changes to DEGRADED and redundancy is reduced, increasing data loss risk.

Environment & Reproduction

Appears after disk media errors, cable faults, or controller instability.

zpool status -v
zpool iostat -v 2
smartctl -a /dev/ada0

Root Cause Analysis

I/O and checksum errors exceed tolerance on one vdev member, forcing faulted or degraded state.

Quick Triage

Confirm pool health and locate affected physical device.

zpool status
camcontrol devlist
geom disk list | head -n 80

Step-by-Step Diagnosis

Map failing GUID to disk serial and inspect SMART trends.

zpool status -g
smartctl -x /dev/ada1
glabel status

Solution – Primary Fix

Replace failed disk and start resilver with monitored progress.

zpool offline tank ada1
zpool replace tank ada1 /dev/ada3
zpool status -v

Solution – Alternative Approaches

If transient, clear errors and run scrub, but only after confirming hardware stability.

Verification & Acceptance Criteria

Pool returns ONLINE with no uncorrectable errors after resilver or scrub.

zpool status
zpool scrub tank
zpool status -v

Rollback Plan

If replacement fails, reinsert original member and restore from backups if needed.

zpool detach tank ada3 || true
zpool online tank ada1

Prevention & Hardening

Schedule regular scrubs and SMART monitoring with proactive disk replacement policy.

Related Errors & Cross-Refs

Often linked with controller resets, flaky power, and UDMA CRC spikes.

Related tutorial: View the step-by-step tutorial for freebsd-12.

View all freebsd-12 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

zpool(8), zfs(8), and FreeBSD ZFS operational guidance.