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Container Volumes: Persistent Storage for Docker and Podman

Containers are ephemeral — when they're removed, data is lost. Volumes solve this by persisting data outside the container lifecycle.

dockervolumesstoragecontainers

The Problem


Containers are designed to be disposable. Stop a container, remove it, start a new one. But what about the data inside?


Without volumes, database data, user uploads, and configuration changes are lost when a container is replaced.


Volume Types


Named Volumes

Managed by Docker/Podman. Data stored in a location managed by the container runtime.


docker volume create mydata

docker run -v mydata:/app/data myimage


  • Pros: Portable, easy to back up, managed lifecycle
  • Cons: Harder to access files directly

    • Bind Mounts

    Mount a host directory into the container.


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


  • Pros: Direct file access, easy to understand
  • Cons: Tied to host filesystem, permission issues common

    • tmpfs Mounts

    In-memory storage. Fast but lost on container stop.


    docker run --tmpfs /app/cache myimage


  • Use for: Caches, temporary files, sensitive data that shouldn't persist

    • Common Patterns


    Database Data

    Always use a named volume for database storage:

    -v postgres_data:/var/lib/postgresql/data


    Never use a bind mount for databases — filesystem semantics can cause data corruption.


    Application Uploads

    Bind mount for user uploads (easy to back up and serve):

    -v /data/uploads:/app/uploads


    Configuration Files

    Bind mount individual config files:

    -v ./nginx.conf:/etc/nginx/nginx.conf:ro


    The :ro flag makes it read-only inside the container.


    Permission Issues


    The #1 volume problem. Container runs as UID 1000, host directory owned by root.


    Solutions:

    1. Match UIDs: Run container with --user matching host UID

    2. chown: Change host directory ownership to match container user

    3. Podman rootless: Podman maps UIDs automatically in rootless mode


    Backup Strategy


    Named Volumes

    docker run --rm -v mydata:/data -v /backups:/backup alpine tar czf /backup/mydata.tar.gz /data


    Bind Mounts

    Back up the host directory directly with rsync, Restic, or Borg.


    On TinyPod


    TinyPod manages volumes for each application automatically. Data persists across container updates and restarts. Backups are handled by the platform.