Oops, yes, that's a good point. Filesystems with fancy things like reflinks probably have their own tools for deduplication.
On 15 February 2015 at 01:48, Wout Mertens <wout.mert...@gmail.com> wrote: > If you want to use reflinks, better to use the deduplication tools that come > with the filesystem, e.g. > https://btrfs.wiki.kernel.org/index.php/Deduplication (duperemove is in > nixpkgs). > > Also, it would be nice if we could patch GNU cp so that it always tries to > use reflinks (so that builds automatically have reflinks where possible). > There's an option "--reflinks=auto" that does that and I don't understand > why it's not the default (as discussed at > http://unix.stackexchange.com/questions/80351/why-is-cp-reflink-auto-not-the-default-behaviour). > Maybe we should make it a nixos option. > > Hardlinks are slightly impure and they do cause build failures in rare and > easily-fixed cases, but they're cross-platform, robust and easy to inspect. > Indeed the .links directory won't be able to be pruned due to reflinks being > invisible. > > To implement reflinks properly you would have to keep a hash of each file in > the nix-store in a DB. This has advantages, like being able to hash lazily > (only when another file with the same size shows up), and being able to do > queries, but it also means that you're duplicating that other DB, the file > system. > > > Wout. > > On Sun, Feb 15, 2015, 9:54 AM James Cook <james.c...@utoronto.ca> wrote: >> >> > Once I wondered if using reflinks instead of hardlinks might be better >> > from >> > some point of view, but it probably won't be a big difference. >> >> I would really like to see reflinks being used instead of hard links >> on filesystems that support it. Hard linking is an impurity which can >> cause bugs, as Wout pointed out at the start of the thread (e.g. >> https://github.com/NixOS/nixpkgs/issues/4266). >> >> Implementation question: how would nix know when it can delete a file >> in /nix/store/.links? I assume than now it just checks the number of >> links, but I don't know if you can do that with reflinks. >> >> James >> _______________________________________________ >> nix-dev mailing list >> nix-dev@lists.science.uu.nl >> http://lists.science.uu.nl/mailman/listinfo/nix-dev _______________________________________________ nix-dev mailing list nix-dev@lists.science.uu.nl http://lists.science.uu.nl/mailman/listinfo/nix-dev