DWARFS

Latest revision as of 23:44, 17 August 2025

Deduplicating Warp-speed Advanced Read-only File System (DWARFS) is a read-only filesystem that optionally supports no compression (via --compress-level=0 or --compression=null for instance) and no deduplication (via --file-hash none).

It is developed by Marcus Holland-Moritz and when compared to Squashfs, DWARFS also offers a choice of hashing algorithms,^[2] as well as a tool for checking DWARFS image via dwarfsck.

At maximum compression levels using LZMA, DWARFS (using --compression=lzma:level=9:extreme) can produce smaller file size compared to SquashFS with the rough equivalent of using XZ as -comp xz.

The software is currently available for both Unix-like (generally Linux) and Microsoft Windows, with the caveat that, "Support for the Windows operating system is currently experimental. Having worked pretty much exclusively in a Unix world for the past two decades, my experience with Windows development is rather limited and I'd expect there to definitely be bugs and rough edges in the Windows code."^[3] There is even homebrew formulae for macOS.

See also Squashfs.

[edit] Discussion

The aim with this software project is to ultimately create a compressed, deduplicated, read-only file system. While it is possible to disable all except for read-only, disabling it defeats the purpose.

DWARFS software project also intends to compete (performance-wise) with SquashFS at file system creation, in that a given directory, folder, or path is scanned, hashed, (optionally categorized) before the contents are compressed, adding only the unique copies. SquashFS tends to add and hash files as it creates the file system, similar to how 7-Zip or ZIP files for instance are created, with the apparent ability to detect and avoid adding duplicate files during creation process that is unique to the likes of SquashFS and DWARFS, which however is considered slower, generally double-handling compared to DWARFS which does these during the scanning phase.

The developer's original motivation was with, "several hundred different versions of Perl that were taking up something around 30 gigabytes of disk space" and that there, "was unwilling to spend more than 10% of my hard drive keeping them around for when I happened to need them."^[4] This may put the project in line for competing with git, which is a Versioning Control System (VCS), that is used to record changes to a given project at a more atomic level, compressing (and using zlib) changes with each commit, however, unlike git which introduces rather steep learning curves, contrasting to just adding several versions of the same software project into an "archive" is arguably more trivial to do. Ultimately, DWARFS, like SquashFS has many other potential use-cases, rather than whatever they were intentionally designed for, making it a somewhat popular choice in the race against other forms of archivers and software/file distribution methods, without requiring the use of bespoke compression software that happens to be ranked among the top in Matt Mahoney's data compression benchmarks.

[edit] Identification

DWARFS files begins with the hexadecimal 44 57 41 52 46 53 which translates to "DWARFS" in ASCII.^[5]

[edit] Examples

Create an extremely compressed DWARFS image, without history, all root owned contents, sha3-512 hash algorithm, idle task (lowest priority) from present directory to example.dwarfs:

 mkdwarfs --input . --output=example.dwarfs --block-size-bits=26 --compression=lzma:level=9:extreme --compress-niceness=10 --schema-compression=lzma:level=9:extreme \
 --metadata-compression=lzma:level=9:extreme --no-history --pack-metadata=all,force --file-hash=sha3-512 --set-owner=0 --set-group=0 --no-history-timestamp \
 --no-create-timestamp --no-history-command-line

[edit] mkdwarfs only features

The following below illustrates features that are only available upon creating the DWARFS file. Once the DWARFS file has been created, the only way to change these is to use --recompress=all.

[edit] Choice of available compression

As of version 0.12.4, the following compressors are available:

[edit] Choice of available hash for duplication detection

Since 0.7.0-RC1 introduced alternatives,^[14] as of version 0.12.4, the following hash algorithms are available:

[edit] Links

• DWARFS project page (GitHub)

[edit] References

1. ↑ Release 0.1.0 - GitHub
2. ↑ Choice of hash for duplicate detection #92 - GitHub
3. ↑ Windows Support section of README.md - DWARFS - GitHub
4. ↑ History section - DWARFS - GitHub
5. ↑ 0000449: Add magic for the DWARFS compressed file system format - bugs.astron.com
6. ↑ null.cpp (line 110) - DWARFS - GitHub
7. ↑ lzma.cpp (line 413) - DWARFS - GitHub
8. ↑ zstd.cpp (line 179) - DWARFS - GitHub
9. ↑ lz4.cpp (line 186) - DWARFS - GitHub
10. ↑ brotli.cpp (line 169) - DWARFS - GitHub
11. ↑ flac.cpp (line 496) - DWARFS - GitHub
12. ↑ rice.hpp (lines 7-9) - compression-algorithms - GitHub
13. ↑ ricepp.cpp (line 260) - DWARFS - GitHub
14. ↑ Choice of hash for duplicate detection #92 post #5 - DWARFS - GitHub
15. ↑ Choice of hash for duplicate detection #92, post #5 - DWARFS - GitHub
16. ↑ Security section of MD5 - Wikipedia
17. ↑ Commit de5ec99 - test/checksum_test.cpp (line 55) - test(checksum): add checksum tests - DWARFS - GitHub
18. ↑ Choice of hash for duplicate detection #92, post #1 - DWARFS - GitHub
19. ↑ Attacks section of SHA-1 - Wikipedia
20. ↑ Commit afbd85e - fix(checksum): disable extended output algorithms (e.g. shake(128|256)) - DWARFS - GitHub
21. ↑ Commit afbd85e - fix(checksum): disable extended output algorithms (e.g. shake(128|256)) - DWARFS - GitHub
22. ↑ Commit 7ded26d - feat(checksum): add hexdigest() method - DWARFS - GitHub
23. ↑ v0.7.0-RC1 - DWARFS releases by tag - GitHub