A right-optimized write-optimized file system


The Bε-tree File System, or BetrFS, is an in-kernel file system that uses Bε-trees to organize on-disk storage. Bε-trees are a write-optimized dictionary, and offer the same asymptotic behavior for sequential I/O and point queries as a B-tree. The advantage of a Bε-tree is that it can also ingest small, random writes 1-2 orders of magnitude faster than B-trees and other standard on-disk data structures. The goal of BetrFS is to realize performance that strictly dominates the performance of current, general-purpose file systems.


  • Our SODA 2020 paper shows how to limit tail-latencies in amortized data structures like Bε-trees.
  • Our FAST 2020 paper extends BetrFS to support efficient copy-on-write clones of files and directories.
  • Our OSDI 2020 paper describes our verified implementation of a Bε-tree.
  • Our SPAA 2020 paper explains how we extend the DAM model to more precisely model hard disks and SSDs, and the implications for data-structure design.


For detailed information and source code, visit the BetrFS website.


2020 Interns

External Researchers

  • Bradley C. Kuszmaul
  • Don Porter
  • Jun Yuan
  • Martin Farach-Colton
  • Michael A. Bender
  • William Jannen