🟡 Medium   ⏱ 5–30 min  Last verified: 19 May 2026
Affected versions: FreeBSD 13

📖 ~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

Scrub progress appears frozen, delaying integrity validation windows.

Environment & Reproduction

More visible on large pools with low random I/O throughput.

zpool scrub

Root Cause Analysis

Heavy fragmentation or competing workload causes very slow forward progress.

Quick Triage

Check active scrub stats and per-vdev I/O pressure.

zpool status  && zpool iostat -v 5

Step-by-Step Diagnosis

Identify slow devices and any checksum/read error growth.

zpool status -v
Illustrative mockup for freebsd-13 — zpool_scrub_status
Scrub progress and throughput metrics — Illustrative mockup — Progressive Robot

Solution – Primary Fix

Reduce competing workload and tune scrub scheduling windows.

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sysctl vfs.zfs.scrub_delay=4 && zpool status
Illustrative mockup for freebsd-13 — zpool_iostat_tuning
I/O tuning during scrub — Illustrative mockup — Progressive Robot

Solution – Alternative Approaches

Pause and resume scrub during off-peak periods only.

Verification & Acceptance Criteria

Scrub completion timestamp updates and no new data errors appear.

Rollback Plan

Revert scrub tuning sysctls to baseline values.

Prevention & Hardening

Schedule scrubs with workload-aware maintenance policy.

Often correlated with latent disk read issues.

Related tutorial: View the step-by-step tutorial for freebsd-13.

View all freebsd-13 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

OpenZFS scrub behavior and performance tuning references.

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