Q: After months of daily Docker builds, your production server's disk is full. You run `docker system prune -af` and reclaim some space, but the disk is still 90% full. `docker system df` shows minimal usage. Where is the hidden disk consumption?

docker system prune only removes objects tracked by the Docker daemon (images, containers, volumes, build cache). If the Docker daemon crashed or was force-killed during container operations, orphaned layer directories can accumulate in /var/lib/docker/overlay2/ that the daemon no longer tracks. *Diagnosis:* Run du -sh /var/lib/docker/overlay2/ and compare with docker system df. A large discrepancy confirms orphaned layers. *Fix:* The safest approach is to stop the Docker daemon (systemctl stop docker), back up any critical volumes, and reset the storage entirely (rm -rf /var/lib/docker). Restarting Docker recreates the directory structure. Re-pull needed images. For prevention, ensure the Docker daemon shuts down gracefully and monitor /var/lib/docker disk usage independently.