Hashsync

About

Hashsync runs a command over SSH and replaces blocks of the command's input or output with references when the receiving host already has those blocks in its indexed files. It matches at any byte offset, so renamed, moved or rebuilt files and older dumps are not resent in full. This reduces bandwidth for tools such as rsync, tar and nix-store export, and the author reports a NixOS update dropping from 1.7 GiB to 0.7 GiB.