LocoFS: a loosely-coupled metadata service for distributed file systems

Key-Value stores provide scalable metadata service for distributed file systems. However, the metadata's organization itself, which is organized using a directory tree structure, does not fit the key-value access pattern, thereby limiting the performance. To address this issue, we propose a distributed file system with a loosely-coupled metadata service, LocoFS, to bridge the performance gap between file system metadata and key-value stores. LocoFS is designed to decouple the dependencies between different kinds of metadata with two techniques. First, LocoFS decouples the directory content and structure, which organizes file and directory index nodes in a flat space while reversely indexing the directory entries. Second, it decouples the file metadata to further improve the key-value access performance. Evaluations show that LocoFS with eight nodes boosts the metadata throughput by 5 times, which approaches 93% throughput of a single-node key-value store, compared to 18% in the state-of-the-art IndexFS.