TABLEFS: Enhancing Metadata Efficiency in the Local File System

File systems that manage magnetic disks have long recognized the importance of sequential allocation and large transfer sizes for file data. Fast random access has dominated metadata lookup data structures with increasing use of B-trees on-disk. Yet our experiments with workloads dominated by metadata and small file access indicate that even sophisticated local disk file systems like Ext4, XFS and Btrfs leave a lot of opportunity for performance improvement in workloads dominated by metadata and small files. In this paper we present a stacked file system, TABLEFS, which uses another local file system as an object store. TABLEFS organizes all metadata into a single sparse table backed on disk using a Log-Structured Merge (LSM) tree, LevelDB in our experiments. By stacking, TABLEFS asks only for efficient large file allocation and access from the underlying local file system. By using an LSM tree, TABLEFS ensures metadata is written to disk in large, non-overwrite, sorted and indexed logs. Even an inefficient FUSE based user level implementation of TABLEFS can perform comparably to Ext4, XFS and Btrfs on data-intensive benchmarks, and can outperform them by 50% to as much as 1000% for metadata-intensive workloads. Such promising performance results from TABLEFS suggest that local disk file systems can be significantly improved by more aggressive aggregation and batching of metadata updates.