HERMES

HERMES, a.k.a. sHallow dirEctory stRucture Many-filE fileSystem, is a filesystem base on FUSE designed for numerous small files with simple directory structure, on which occasion common file systems has a serious performance degradation.

Authors & License

The authors of HERMES are listed below:

• Shengqi Chen
• Jiajie Chen
• Xiaoyi Liu
• Jian Gao

This project is an assignment of Basics of Stroage Technology course, Spring 2019, Tsinghua University. All code created by the authors is licensed under the MIT license, while open source code used in this project is subjected to their own licenses.

Dependencies

Project

• clang++ >= 7.0
• gcc >= 5.0
• CMake >= 2.8

Backends

HERMES supports several key-value databases as its backend, and you can choose one when configuring cmake project. LevelDB will be used as the default backend if you do not specify one. According to your choice, HERMES would depends on one of:

• LevelDB >= 1.20
• RocksDB >= 5.8.8
• BerkeleyDB >= 5.3.28
• Vedis: no dependencies (using git-submodule to download source automatically)

You can either install prebuilt development packages (such as libleveldb-dev) or compile and install them manually. See CMakeModules/*.cmake for how to specify non-default library locations.

Compilation & Running

mkdir build && cd build
CXX=clang++ cmake .. -DBACKEND=[LevelDB/RocksDB/BerkeleyDB/Vedis]
cmake --build .

The executable can be located at build/src/HERMES.

Besides common fuse options, filesystem-specific options are:

--metadev=/path/to/meta # location to save the metadata
--filedev=/path/to/file # location to save the file content

Note that different backends requires different types metadev and filedev. LevelDB and RocksDB need directories, while BerkeleyDB and Vedis need files.

You can use --help to see the complete help text and --version to see the compilation time and backend version of HERMES.

Tests

There are several tests in tests directory:

• read_write_perf.sh: Test the read & write performance of different backends.
• file_list_perf.sh: Test the performance of file creation & enumeration of different backends.
• test_correctness.sh: Test the implementation correctness of different backends.

The first two tests requires fio to run, and will generate reports in results directory.

Implementation

You may refer to doc/report.pdf for more details (in Chinese).