Mono-repo Vs. Hybrid: What’s the Right Approach? The benefits of using a monorepo vs. multi-repos are tremendous, but you need to be aware of the difficulties that surface when the projects start to scale up. Facebook built its own custom filesystem (used fuse file system) and source control (fbsource — customized Mercurial) in order to address the scale-up issues. We decided to break the monolith and move to microservices. If projects were dependent on each other, the coupling became only API contracts.