How to fix devmapper: Thin Pool has free data blocks which is less than minimum required in Docker

First, examine the current state of your thin pool:

docker info | grep -A 20 "Storage Driver"

Look for these key values:
- Data Space Used / Data Space Total: How much of the thin pool is consumed
- Thin Pool Minimum Free Space: The threshold that triggers this error

Also check LVM thin pool status directly:

sudo lvs

This shows the data percentage used for each logical volume.

Remove unused containers, images, and volumes to free space:

# Remove stopped containers
docker container prune -f

# Remove unused images
docker image prune -a -f

# Remove unused volumes
docker volume prune -f

# Or clean everything at once
docker system prune -a --volumes -f

Note: On some systems with devicemapper issues, pruning may not immediately recover thin pool space. You may need to restart Docker after pruning:

sudo systemctl restart docker

If pruning doesn't recover space due to orphaned layers, try saving active images and reloading them:

# Save important images to tar files
docker save -o myapp.tar myapp:latest

# Remove all images
docker rmi $(docker images -q) -f

# Reload the images you need
docker load -i myapp.tar

This creates fresh image layers without orphaned data.

If your volume group has free space, extend the thin pool:

# Check available space in the volume group
sudo vgs

# Extend the thin pool (adjust the path based on your setup)
sudo lvextend -l+100%FREE /dev/docker/thinpool

If the thin pool name is different, find it with:

sudo lvs -a | grep pool

After extending, verify Docker recognizes the new space:

docker info | grep "Data Space"

Enable automatic thin pool extension to prevent future issues. Create or edit the LVM profile:

sudo vi /etc/lvm/profile/docker-thinpool.profile

Add these settings:

activation {
  thin_pool_autoextend_threshold=80
  thin_pool_autoextend_percent=20
}

This extends the pool by 20% when usage reaches 80%. Apply the profile:

sudo lvchange --metadataprofile docker-thinpool docker/thinpool

As a temporary fix, you can lower the minimum free space threshold:

sudo systemctl stop docker

Edit or create /etc/docker/daemon.json:

{
  "storage-opts": [
    "dm.min_free_space=5%"
  ]
}

Restart Docker:

sudo systemctl start docker

Warning: Lowering this threshold too much risks thin pool exhaustion and potential data corruption. Use this only as a temporary measure while implementing a permanent fix.

The devicemapper driver is deprecated. Migrating to overlay2 provides better performance and avoids thin pool issues:

Warning: This process removes all existing images and containers. Back up important data first.

# Stop Docker
sudo systemctl stop docker

# Back up Docker data (optional)
sudo cp -au /var/lib/docker /var/lib/docker.backup

# Remove old Docker data
sudo rm -rf /var/lib/docker

# Configure overlay2 in daemon.json
sudo vi /etc/docker/daemon.json

Set the storage driver:

{
  "storage-driver": "overlay2"
}

Start Docker:

sudo systemctl start docker
docker info | grep "Storage Driver"

You'll need to re-pull all images after migration.