Docker Volumes & Storage

When I started learning Docker, everything was smooth until I hit this question:

“Where does my data go when the container stops?”

At first, I didn’t think much about it.
Then one day I stopped a container… and my data was gone.

That’s when I realized:

Containers are temporary. Data is not.

So this blog is about:

• Why Docker volumes exist

• What problem they solve

• Types of storage (bind mount vs volume)

• Commands (real ones I used)

• Simple Ubuntu examples

No theory overload. Just what actually matters.

🔹 The Real Problem

When you run a container:

docker run ubuntu

You’re inside a completely isolated environment.

You create files:

touch file.txt

Now exit and remove container:

docker rm <container_id>

Boom 💥

Your file is gone.

Because:

Container filesystem = temporary

🔹 Why We Need Volumes

We use volumes when:

• We don’t want data to disappear

• We want to share data between containers

• We want to connect container with host files

In simple words:

Volumes = permanent storage for containers

🔹 Two Types of Storage (Very Important)

1️⃣ Bind Mount (Host → Container)

This directly connects your local folder to the container.

docker run -v /home/ubuntu/data:/app ubuntu

Meaning:

HOST DIR → CONTAINER DIR

So:

• Anything inside /app is actually stored on your host

• Changes reflect instantly

Example (Ubuntu)

docker run -it -v /home/ubuntu/test:/data ubuntu

Inside container:

cd /data
touch hello.txt

Now check on host:

ls /home/ubuntu/test

You’ll see:

hello.txt

👉 This is real-time sync

When to use Bind Mount

• Development

• Debugging

• Live code changes

• Sharing files with host

🔹 2️⃣ Docker Volume (Managed by Docker)

This is created and managed by Docker itself.

Create volume

docker volume create myvolume

Use volume

docker run -it -v myvolume:/data ubuntu

Now:

• Data is stored by Docker internally

• Not directly visible like normal folders

Inspect volume

docker volume inspect myvolume

Remove volume

docker volume rm myvolume

Clean unused volumes

docker volume prune

⚠️ This deletes all unused volumes

🔹 What’s the difference?

🔹 Important Commands (Grouped)

Volume commands

docker volume create VOL_NAME
docker volume rm VOL_NAME
docker volume inspect VOL_NAME
docker volume prune

Using volumes in container

docker run -v VOL_NAME:/container/path
docker run -v /host/path:/container/path

Inspect container (to see mounts)

docker inspect CONTAINER_ID

You’ll see:

• Volume path

• Mount info

• Bind details

🔹 Small Mistake I Made (Learn from it)

At first I used:

docker run -v MOUNT_PATH

This is incomplete ❌

Correct format is:

docker run -v HOST_DIR:CONTAINER_DIR

Example:

docker run -v /home/ubuntu/data:/app

🔹 Real Understanding (This Changed Everything)

Before:

• I thought container = like VM

After:

• Container = temporary process

• Volume = actual storage

So now my thinking is:

App runs in container
Data lives in volume

🔹 When I Use What

Bind Mount

• While coding

• When I want live reload

• When I want to see files directly

Docker Volume

• Database (Mongo, MySQL)

• Production apps

• Persistent storage

🔹 Reference (If you want to go deeper)

While learning this, I also checked the official Docker docs to understand things more clearly.

If you want to explore in detail:

https://docs.docker.com/engine/storage/volumes/

It explains:

• How Docker manages volumes internally

• Advanced volume options

• Production-level usage

🔑 One Line That Made It Click

Containers are temporary, volumes are permanent.