Docker Volume Mounts with -v Flag

Persistent Data with Docker Volumes

Container filesystems are ephemeral -- when a container is removed, all data inside it is lost. Docker volumes provide persistent storage that survives container restarts and removals.

Creating and Using Named Volumes

docker run -d --name db -v pgdata:/var/lib/postgresql/data postgres:16

This creates a named volume called pgdata (if it does not already exist) and mounts it at /var/lib/postgresql/data inside the container. PostgreSQL stores its data files in this directory, so they persist even if the container is removed and recreated.

Volume Lifecycle

Named volumes are managed independently from containers:

docker volume create mydata           # Create explicitly
docker volume ls                       # List all volumes
docker volume inspect pgdata           # Show volume details
docker volume rm pgdata                # Remove a volume
docker volume prune                    # Remove unused volumes

Volumes persist until explicitly removed. Removing a container does not remove its associated volumes.

Sharing Volumes Between Containers

Multiple containers can mount the same volume simultaneously:

docker run -d --name writer -v shared-data:/data my-writer-app
docker run -d --name reader -v shared-data:/data my-reader-app

Both containers see the same files in /data. This enables patterns like:

• A web server and a content management system sharing a static files directory.
• A log writer and a log processor sharing a log directory.

Volume Mount Syntax

The -v flag (and the more verbose --mount) support several formats:

# Named volume
-v volume-name:/container/path

# Named volume with read-only access
-v volume-name:/container/path:ro

# Anonymous volume (auto-generated name)
-v /container/path

# Using --mount (more explicit)
--mount type=volume,source=volume-name,target=/container/path

Volumes vs. Bind Mounts

Feature	Named Volume	Bind Mount
Managed by Docker	Yes	No
Location on host	Docker-controlled (/var/lib/docker/volumes/)	Any host path
Pre-populated	Yes (copies image content)	No (overwrites with host content)
Backup	docker volume commands	Standard file tools
Performance on macOS/Windows	Optimized	Slower (filesystem translation)

When to Use Named Volumes

• Database storage (PostgreSQL, MySQL, MongoDB data directories)
• Application state (file uploads, generated files)
• Shared data between related containers
• CI/CD caches (node_modules, build artifacts)

Backup and Restore

Back up a volume by mounting it in a temporary container:

docker run --rm -v pgdata:/data -v $(pwd):/backup ubuntu tar czf /backup/pgdata.tar.gz -C /data .

Restore by extracting the archive into the volume:

docker run --rm -v pgdata:/data -v $(pwd):/backup ubuntu tar xzf /backup/pgdata.tar.gz -C /data