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Diagnose Container Storage Size

Overview​

Docker storage reporting can be confusing if you mix container writable layer, image size, and volume data.

Key Concepts​

  • SIZE: writable layer growth per container
  • VIRTUAL SIZE: image size plus writable layer
  • volumes are outside container writable layer accounting

Commands​

docker ps -s
docker system df
docker system df -v
docker container inspect <container> --format='{{.SizeRw}}'
docker container inspect <container> --format='{{.SizeRootFs}}'

Common Misunderstanding​

Large virtual size does not mean duplicated image bytes per container. Shared image layers are stored once.