Explain what OverlayFS is and how it is used in Docker to organize container data storage.

OverlayFS is a union type of filesystem that allows combining multiple layers into a single virtual filesystem layer. In Docker, OverlayFS is used to organize image and container layers, enabling efficient storage and management of data.

How it works in Docker:

• Each Docker image consists of multiple layers (read-only).
• When a container is started, Docker creates a writable layer (read-write) on top of these layers.
• OverlayFS merges these layers into a single filesystem space, where container changes are written to the top layer.

Advantages:

• Saves space, as image layers are shared among containers.
• Fast container creation through layer reuse.

Example:

• An image consists of layers A, B, C (read-only).
• A container is launched with a writable layer D on top.
• OverlayFS combines A+B+C+D into a single filesystem layer for the container.

Thus, OverlayFS provides efficient and flexible data storage in Docker.