RegionCast

Players and operators pick regions on a map of the world instead of typing coordinates and hoping the right file was chosen. The map shows tiles of 512 by 512 blocks, and a zoomed-in view switches to a grid of regions and then single chunks. Changed regions are coloured in a ledger that compares two files, so only the parts that differ are marked for copying. The mod lives inside the Minecraft process and cannot stop the server by itself, so the server must be shut down for the copy to run.

Before copying, the source server is told to save and flush its data over RCON with save-off and save-all. Chunks that cross a border arrive half lit until the game recalculates lighting, and copying is slower per block because each chunk is decompressed and recompressed. Copying 60 regions at once takes roughly the disk space those regions occupy, around 400 MB. A second server can mirror a build server, so a creative test world can show a base to people without letting them touch the real one. Installation needs Fabric API on Fabric. RegionCast is server required and client optional, and the MIT License covers the open source code for version 26.3 and the 1.21 builds.