Zchunk

Zchunk is a format for compressing files in a way that is well-suited for synchronizing two copies of a file over a network; as well as a program that performs this syncronization. Arguably this problem was already solved by the older Rsync system, but due to the widespread adoption of HTTP for non-Web communications purposes, it cannot always be used. Zchunk first splits the file into a number of "chunks"; then compresses these chunks individually, so that, after a comparison has been made between the copies of the receiver and sender, only the changed chunks need to be downloaded. Unlike some similar formats, Zchunk concatenates all the chunks together, along with a header, into a single file.

Zchunk was developed in order to allow the Fedora Linux distribution to use less bandwidth when its software updater was downloading metadata.

Zstd compression is currently (2020) the only format supported; and Zchunk also supports an embedded PGP signature.

Identification
Version 1 Zchunk files (as of 2020 the only version that exists) begin with.

Specifications

 * zchunk_format.txt

Software

 * Main implementation

Links

 * Introducing zchunk
 * What is zchunk?