Because macOS does not run a native Linux kernel, Docker Desktop executes within a lightweight virtual machine. That virtual machine stores all containers, images, and volumes inside a single large virtual disk file: Docker.raw.
The Non-Shrinking Sparse File Problem
When you pull a 5GB Docker image, Docker.raw expands to fit it. However, when you delete that image with docker rmi, the virtual disk file does not shrink automatically on macOS APFS. It remains allocated at its peak size (frequently 64GB).
XrayMac detects Docker virtual disk bloat, compares actual container payload with allocated disk size, and provides automated compacting to reclaim space without losing vital volumes.