Managing Docker storage efficiently is becoming more important as cloud-native workloads scale and disk usage grows rapidly. Teams running Docker on cloud VMs often hit a common bottleneck: the root disk fills up quickly with images, containers, logs, and volumes.

While Docker defaults to storing everything under /var/lib/docker, this can cause multiple issues:

• The OS disk becomes unusable
• Containers fail during builds
• Disk I/O slows down the entire VM
• Upgrades and backups become risky

But here's the good news: Docker doesn’t need to store data in /var/lib/docker.
You can easily migrate everything to an external attached disk, mounted anywhere, and configure Docker to use that new storage path.

This guide walks through the complete process of mounting an external disk at a custom path and migrating the Docker data-root, without overwriting the system directory.
This is the cleanest, safest way to expand Docker storage, used in production by DevOps teams across clouds.
Let’s begin.

Step-by-Step Guide

Step 1 — Identify the external disk

lsblk

Find the unmounted disk (e.g., /dev/sda).

Step 2 — Format the disk

sudo mkfs.ext4 /dev/sda

Step 3 — Create mount point

sudo mkdir -p /mnt/docker-storage

Step 4 — Mount the disk

sudo mount /dev/sda /mnt/docker-storage

Verify:

df -h | grep docker-storage

Step 5 — Persist the mount

echo '/dev/sda /mnt/docker-storage ext4 defaults 0 0' | sudo tee -a /etc/fstab

Step 6 — Stop Docker

sudo systemctl stop docker

Step 7 — Copy existing Docker data (if any)

sudo cp -a /var/lib/docker/* /mnt/docker-storage/

If empty, skip—safe.

Step 8 — Point Docker to the new data-root

sudo mkdir -p /etc/docker
echo '{"data-root": "/mnt/docker-storage"}' | sudo tee /etc/docker/daemon.json

Step 9 — Start and verify

sudo systemctl start docker
docker info | grep "Docker Root Dir"

Expected:

Docker Root Dir: /mnt/docker-storage

Test with:

docker pull nginx

Check size:

sudo du -sh /mnt/docker-storage

4. Why This Option Is Better Than Mounting Over /var/lib/docker

Using a dedicated mount path provides better control, avoids conflicts with system directories, and offers a clean separation between OS-level storage and Docker data.

Conclusion

Moving Docker storage to an external disk is one of the simplest ways to improve performance, reliability, and scalability on any cloud VM or bare-metal server.
By attaching a new disk, mounting it at a dedicated path, and updating Docker’s data-root configuration, you gain:

• A clean separation between OS and Docker
• Zero-downtime migration
• Flexible storage layout
• Better disk performance
• Safer long-term maintenance

Whether you're optimizing a development server or preparing a production deployment, this method gives Docker the storage space it needs—without touching critical system directories..