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Comment by pikdum | Hacker News Reader

Neat! Would a similar approach work with ZFS instead of btrfs?

With btrfs, you can freely create subvolumes and snapshots anywhere (including nested inside of each other), you can have thousands of them without any noticeable performance impact, and you can easily convert a snapshot to a writable subvolume. I don't have much experience with ZFS, but from reading another post [0], my impression is that this isn't really doable with ZFS. And based off of rift's Readme, I think that these features are required for it to work. But I'm not an expert, so I may be mistaken about something here.

[0]: https://news.ycombinator.com/item?id=45077119

How about cp --reflink? Supported by btrfs, bcachefs and zfs. It's quite not as fast as subvolumes in btrfs, but it should be plenty fast.

This should actually be a feature for git itself, if it's not already.

That reflinks the files, which should get you the space savings, but I'm pretty sure that that still has to recursively copy every file in the directory, which can be fairly slow if you have tens of thousands of files, whereas btrfs snapshots can reflink the directory itself, so it should be faster.

Buy yeah, this should be equivalent in most cases, since I can't imagine that many Git repos have enough files for the difference to be noticeable.

I don't have a reflink-able filesystem in this host, but I just tested that

    echo 2 | sudo tee /proc/sys/vm/drop_caches
    time cp -rl foo bar

took 2.6 seconds for 273000 files, so I think it's highly manageable. Reflinking might be a bit slower than hardlinking, though.

Also you can create and destroy (assuming the 'user_subvol_rm_allowed' mount option) BTRFS subvolumes without being root.

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