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I worked with dedupe products at a previous job. Media files generally deduplicate poorly.

Uncompressed Blu-ray rips are almost the same size when compressed with lossless compression. The binary content of h264 files are almost random bits so deduplication is almost a waste of CPU time. Maybe you can save space from the useless repeated media like trailers and other ads in the bluray isos

You should maybe read about the use cases for deduplication before using it. Here's one recent article:

https://despairlabs.com/blog/posts/2024-10-27-openzfs-dedup-is-good-dont-use-it/

If you mostly store legit Blu-ray rips, the answer is probably no, you should not use zfs deduplication.

I think the universal consensus is that outside of a very specific use case: multiple VDI desktops that share the same image, ZFS dedupe is completely useless at best and will destroy your dataset at worst by causing to be unmountable on any system that has less RAM than needed. In every other use case, the savings are not worth the trouble.

Even in the VDI use case, unless you have MANY copies of said disk images(like 5+ copies of each), it’s still not worth the increase in system resources needed to use ZFS dedupe.

It’s one of those “oooh shiny” nice features that everyone wants to use, but will regret it nearly every time.

Like most have said it is best to stay away from ZFS deduplication. Especially if your data set is media the chances of an entire ZFS block being the same as any other is small unless you somehow have multiple copies of the same content.

Imagine two mp3s with the exact same music content but with slightly different artist metadata. A single bit longer or shorter at the beginning of the file and even if the file spans multiple blocks ZFS won't be able to duplicate a single byte. A single bit offsetting the rest of the file just a little is enough to throw off the block checksums across every block in the file.

To contrast with ZFS, enterprise backup/NAS appliances with deduplication usually do a lot more than block level checks. They usually check for data with sliding window sizes/offsets to find more duplicate data.

There are still some use cases where ZFS can help. Like if you were doing multiple full backups of VMs. A VM image has a fixed size so the offset issue above isn't an issue, but if beware that enabling deduplication for even a single ZFS filesystem affects the entire pool, even ZFS filesystems that have deduplication disabed. The deduplication table is global for the pool and once you have turned it on you really can't get rid of it. If you get into a situation where you don't have enough memory to keep the deduplication table in memory ZFS will grind to a halt and the only way to completely remove deduplication is to copy all of your data to a new ZFS pool.

If you think this feature would still be useful for you, you might want to wait for 2.3 to release (which isn't too far off) for the new fast dedup feature which fixes or at least prevents a lot of the major issues with ZFS dedup

More info on the fast dedup feature here https://github.com/openzfs/zfs/discussions/15896

ZFS dedup is memory constrained, and the memory use scales with the block hashes.

If performance isn't a concern, you're better off compressing your media. You'll get similar storage efficiency with less crash consistency risk.

Something like fslint might be what you want. Scan folders, lists duplicates, you set how you want to deal with them. Its more manual, but I think it is what you are actually trying to achieve.

I haven’t tried it because I’ve read a lot of negative discussions of it—and because (by my understanding) the only reasonable use case would be if there were a large number of users and each user is likely to have copies of the same files but don’t want to expose their files to each other (so you can't just manually de-dupe).