The original title is "OverlayFS Explained: How Docker's Filesystem Layers Actually Work"

Short summary

OverlayFS is a Linux union filesystem that powers Docker's image layering by stacking read-only lower layers with a writable upper layer, creating a unified view without data merging. Modifications use copy-on-write (CoW) to copy files to the upper layer while keeping lower layers unchanged. This mechanism enables Docker to build efficient, layered images where only modified files consume additional disk space.

• •OverlayFS uses read-only lower layers plus a writable upper layer to create a unified filesystem view
• •Copy-on-write ensures modifications don't affect lower layers, only the upper writable layer
• •Docker's layered image architecture depends on this mechanism for space-efficient container building

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