thunderdup

thunderdup - Fast concurrent linux file deduplicator

How to use:

$ time thunderdup
Scanning ...
2024-05-03 06:58:10:
	unique:    276	173 MiB
	duplicate: 2	213 KiB
	queue length: 0
	currently working workers: 0/192
Deduplicating ...
deduplicating: docs/examples/example-folder/ipfs.paper.draft3.pdf
	- docs/examples/example-folder/test-dir/ipfs.paper.draft3.pdf
deduplicating: .git/hooks/pre-rebase.sample
	- test/sharness/lib/sharness/.git/hooks/pre-rebase.sample
total dedupped: 426 KiB
dedupping errors: 0

________________________________________________________
Executed in   73.64 millis    fish           external
   usr time  179.56 millis  621.00 micros  178.94 millis
   sys time   83.87 millis   80.00 micros   83.79 millis

This is a non incremental file deduplicator, tested on btrfs.

How to install

With go installed

go install github.com/Jorropo/thunderdup@latest

Or run as a one shot script:

go run github.com/Jorropo/thunderdup@latest

thunderdup vs bees

I was using bees but it wasn't fitting my usecase very well.

Advantages over bees:

• Faster (reliable 4GiB/s on my Ryzen 3600 with raid1 × 2 NVME).
• Written in a memory safe language (hopefully never matter).
• Easier to use (just go to the directory and run it).
• More granular dedup (dedup selected files or directories recursively instead of whole filesystem)
• File based dedup, does not shard or move extents around on disk,
  • less fragmentation compared to block based dedup
  • less wear on SSDs.
  • *shouldn't be undeduped by btrs fi defrag.
• Perfect deduplication, no probabilistic hash table that lead to partial deduplication of data.

Disadvantages over bees:

• Unbounded memory use, bees use a probabilistic hash table which let it to use a fixed amount of memory at the cost of deduping accuracy, thunderdup stores all the files scanned and their hash in memory, it will crash if you have too much files compared to your amount of ram.
• Non incremental, require full scan on each time, more realistically this is usefull as a one shot tool.
• Less to none workarounds for kernel btrfs bugs. I didn't got any issue on my Linux 6.8.8 and 6.1.0 installs but this is very likely less stable than bees on previous kernels.
• File based dedup, bees can dedup files which only have partial overlaps.

*needs investigation to make sure this doesn't work by accident, I tried it once and it worked properly.

Q&A

Is it safe ?

thunderdup is written in a memory safe language (Go) and open all the files in Read-Only mode, deduplication happens using linux's FileDedupeRange syscall which atomically compare file content in the kernel.

This create reflinks which are Copy-On-Write that means the files share the on disk storage, however when one of them has modified regions they are written into a new location, this means other files are not affected.

Assuming there are no bugs in the kernel, the worst that can happen is dedup not happening where it should have, it can't corrupt or change the content of your files.

It is also possible to have a bug in Go or thunderdup itself, but that less likely.