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OLFS, the Online Layered Filesystem, is a FUSE-based filesystem that supports intra-volume directory layering with hierarchical, inheritance-like namespace unification. While each layer of an OLFS volume constitutes a subvolume that can be mounted separately in a fan-in configuration, the entire hierarchy is always accessible (online) and fully navigable through any mounted layer.
OLFS uses a relational database to store its layering metadata and either a relational database or any (virtual) host file system as its backing store, along with metadata and block caching for improved performance. Because OLFS runs as a virtual file system in user-space, its capabilities are available to all existing software without modification or special privileges. We have developed a reference implementation of OLFS for FUSE based on MySQL and XFS, and conducted performance benchmarking against XFS by itself.
We explore several applications of OLFS, such as enhanced server synchroniz
