What file system is used when working with Docker containers?

Docker uses different file systems to organize image and container layers, depending on the storage driver. The most common drivers are OverlayFS (overlay2), aufs, btrfs, zfs, and devicemapper.

In practice, the overlay2 driver, based on OverlayFS, is most frequently used — it is a modern and efficient mechanism for combining multiple file system layers into one. It provides fast container creation and deletion, space savings through layering, and good performance.

Example: when launching a container, Docker creates an upper layer (read-write) on top of the image layers (read-only), using OverlayFS to combine them into a single container file system.