ChunkSqueeze

Lossless Minecraft chunk compression, reducing terrain storage by around 30% on average.

The more you explore, the larger your world grows. ChunkSqueeze is designed for modpacks, long-running survival worlds, and servers. It combines a compact storage format with shared data to reduce the disk space used by terrain chunks.

It preserves block positions, full block properties, lighting, biomes, and mod NBT data stored in terrain chunks, without changing your world's content or gameplay.

Features

• Compact region files: Uses the .cqs region format to reduce wasted space caused by the 4 KiB allocation units in vanilla .mca files.
• Shared block states: Shares block states and their properties within each region, avoiding repeated storage of the same information across chunks.
• Lossless section deduplication: Shares storage only when entire section data is identical, preserving section height, lighting, biomes, and all other fields.
• Background optimization: Persists complete chunk data to disk first, then optimizes its size in background threads to reduce compression work blocking foreground saves.
• Existing world migration: Includes administrator commands to convert existing terrain regions, check progress, and safely cancel migration.
• Standard world export: Includes offline tools to restore compact worlds to the standard MCA format.

How much space can it save?

On the official server of Tensura Neo Otherworld, using ChunkSqueeze reduced the total size of the world folder from 150 GB to 90 GB.

The following results come from fixed-sample tests of version 0.6.0, using 20 regions and 20,480 chunks per dimension. File sizes include indexes, dictionaries, internal fragmentation, and other storage overhead.

After explicit compaction, terrain file sizes decreased by approximately 32%, 28%, and 37%, respectively. Normal saves trigger compaction based on fragmentation thresholds, so everyday use may not immediately reach the sizes in the final column.

Actual savings depend on terrain, mod content, and how densely regions are populated. These figures apply to terrain region files, not the entire world folder. Sparse regions containing only a few chunks may grow because of fixed index overhead.

Compression requires additional CPU and I/O work. Background optimization can shorten foreground waits, but does not guarantee higher FPS, TPS, or faster terrain generation.

Commands

Players cannot join during migration. Migration processes terrain MCA files only in dimensions currently loaded by the server, and skips regions with no net space savings.

Back up your entire world before migrating. Once each region has been validated and successfully committed, its original MCA and associated MCC files are deleted. Migration does not keep automatic backups. In singleplayer, forcibly disconnecting the local player may shut down the integrated server, so offline conversion tools are recommended for singleplayer worlds.

Compatibility and removal

ChunkSqueeze handles terrain chunk storage. Entity and POI regions retain their original formats. Block states are stored using registry names and full properties, without relying on runtime block IDs. Version 0.6.0 passed block state and persistence checks across restarts in an ATM10 8.5 production server environment, but this does not cover every mod combination or gameplay scenario.

Before removing the mod, you must restore your world to the standard MCA format. Vanilla Minecraft and map editors that only support MCA cannot directly read CQS files. Restoration is also required before downgrading to a version that does not support the current format. Disabling compactRegions alone does not convert existing CQS files.

After stopping the game or server, use tools/restore_world.py, included in the project source, to export a standard world. The tool requires Python 3.10 or later, with no third-party dependencies. The destination directory must not already exist, and the source world is left unchanged. Run this from the project directory:

python -I -X utf8 tools/restore_world.py "D:/CompactWorld" "D:/StandardWorld"

Back up all files in the world directory, and make sure your backup tool includes CQS files and their supporting files. Do not modify world files with external tools while the game or server is running.