[rwarfield]

Isn't it better to use `nix store optimise` for dedup of the nix store? The nix command has more knowledge of the structure of the nix store so should be able to do a better job with fewer resources. Also the store is immutable so you don't actually need reflinks - hard links are enough.

[Filligree]

It is, yeah, though you have to turn it on. I'm not actually sure why it's off by default.

[amarshall]

It’s off by default as it can make builds slower (regardless of platform)—you should test this if you care. There also are (or were) some bugs on macOS that would cause corruption.