Ubuntu 26.04 LTS – LVM thin pool reaches 100% and new writes fail

📖 ~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

Administrators observe: Ubuntu 26.04 LTS – LVM thin pool reaches 100% and new writes fail. VM and container storage operations halt.

Environment & Reproduction

Issue appears with thin-provisioned volumes lacking auto-extend policy.

# Baseline context
lsb_release -a
sudo lvs -a -o +seg_monitor,data_percent,metadata_percent
sudo vgs
sudo pvs
df -h

Root Cause Analysis

Thin pool data or metadata saturation prevents allocation for dependent logical volumes.

Quick Triage

Identify overcommitted thin volumes and immediate freeable capacity.

# Quick triage
sudo lvs -a -o lv_name,lv_size,data_percent,metadata_percent,vg_name
sudo fstrim -av || true
sudo journalctl -k -n 120 --no-pager | grep -Ei 'thin|dm-' || true

Step-by-Step Diagnosis

Check VG free extents and thin pool autoextend settings.

# Detailed diagnosis
sudo vgs -o vg_name,vg_free,vg_size
sudo lvmconfig --type full activation/thin_pool_autoextend_threshold activation/thin_pool_autoextend_percent
cat /etc/lvm/lvm.conf | grep -n 'thin_pool_autoextend'

Solution – Primary Fix

Extend thin pool and enable autoextend threshold to prevent recurrence.

# Primary fix
sudo lvextend -L +20G /
sudo lvextend --poolmetadatasize +1G /
sudo lvs -a -o +data_percent,metadata_percent
sudo sed -i 's/^s*#?s*thin_pool_autoextend_threshold.*/	thin_pool_autoextend_threshold = 70/' /etc/lvm/lvm.conf
sudo sed -i 's/^s*#?s*thin_pool_autoextend_percent.*/	thin_pool_autoextend_percent = 20/' /etc/lvm/lvm.conf

Solution – Alternative Approaches

Delete stale snapshots and reclaim space if extending storage is not immediate.

# Alternative
sudo lvs -a | grep snap
# Remove unneeded snapshots carefully
# sudo lvremove /

Verification & Acceptance Criteria

Thin pool usage remains below alert threshold and writes succeed.

# Verify
sudo lvs -a -o +data_percent,metadata_percent
touch /var/tmp/lvm-thinpool-write-test
sudo journalctl -k -n 80 --no-pager | grep -Ei 'thin|I/O error' || true

Rollback Plan

If extension fails, freeze writes and restore from snapshots/backups.

# Rollback
# Stop write-heavy services
sudo systemctl stop docker || true
# Restore from storage snapshot if available

Prevention & Hardening

Monitor thin pool data and metadata percentages with proactive alerts.

# Hardening
sudo lvs -a -o lv_name,data_percent,metadata_percent
# Integrate with monitoring thresholds

Related Errors & Cross-Refs

Related patterns include device mapper no space left and thin pool metadata full warnings.

Related tutorial: View the step-by-step tutorial for Ubuntu 26.04 LTS.

View all Ubuntu 26.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

LVM thin provisioning administration docs and Ubuntu storage operations guidance.