How to Not Copy Files

Making logical copies, or clones, of files and directories is critical to many real-world applications and workflows, including backups, virtual machines, and containers. In this article, we explore the performance characteristics of an ideal cloning implementation; we show why copy-on write induces a trade-off that prevents existing systems from achieving the ideal constellation of performance features; and we show how to achieve strong cloning performance in an experimental file system, BetrFS.