Do Btrfs or ext4 offer this?
1. Snapshot LVM volume
2. Mount the LVM volume and back the snapshot up somewhere else
3. Delete the snapshot as soon as possible
Otherwise you're going to lose a ton of performance.
[0] https://www.percona.com/blog/disaster-lvm-performance-in-sna...
But, it still has to duplicate metadata which depending on the amount of files may cause inconsistency in the snapshot.
The Arch wiki says:
"Tools dedicated to deduplicate a Btrfs formatted partition include duperemove, bees, bedup and btrfs-dedup. One may also want to merely deduplicate data on a file based level instead using e.g. rmlint, jdupes or dduper-git. For an overview of available features of those programs and additional information, have a look at the upstream Wiki entry.
Furthermore, Btrfs developers are working on inband (also known as synchronous or inline) deduplication, meaning deduplication done when writing new data to the filesystem. Currently, it is still an experiment which is developed out-of-tree. Users willing to test the new feature should read the appropriate kernel wiki page."
It's a similar effect only if you don't modify the files, I think.
If you "clone" a file with a hard link and you modify the contents of one copy, the other copy would also be equally modified.
As far as I understand this wouldn't happen with this type of block cloning: each copy of the file would be completely separate, except that they may (transparently) share data blocks on disk.
This should end up being exposed through cp --reflink=always, so you could look up filesystem support for that.