Fix corrupted chunks and region files

Part of your world is damaged. The Console shows lines such as Failed to read chunk or Region file ... has truncated header. Minecraft stores the world in region files, and each one covers an area of up to 512 by 512 blocks, so one damaged file affects that area while the rest of the world is untouched. Find the file first, then repair it with the least loss.

Checked against Minecraft 26.3 (Mojang's server files), the Paper documentation and minecraft.wiki, October 2026.

What the log says

Open the Console tab, or press Download Log and choose Last hour, and look for one of these:

• Region file <path> has truncated header, has invalid sector at index or Chunk [x, z] is allocated, but stream is missing. The region file itself is damaged.
• Failed to read chunk [x, z]. Minecraft could not load that chunk.
• Chunk file at <path> is missing level data, skipping. That chunk file has no level data in it, and the game skipped it.
• Chunk file at <path> is in the wrong location; relocating. The game found a chunk file stored in the wrong place and is moving it to the right one.
• ChunkNibbleArrays should be 2048 bytes not: 0. This comes from the code that upgrades old chunks to the current format. It reports a data array of 0 bytes where 2048 are expected.

If the message is about level.dat instead, see Fix No key dimensions in MapLike (level.dat).

Find the region file

Region files are named r.X.Z.mca and each holds a 32 by 32 block of chunks, which is 512 by 512 blocks. If the message gives a path, you have the name. If it gives only a chunk such as [-70, 41], divide each number by 32 and round down: -70 becomes -3 and 41 becomes 1, so the file is r.-3.1.mca.

Open the File Manager and go into your world folder. It is world unless you changed World folder in the Config Editor. The path depends on the game version:

• Minecraft 26.1 and later on Vanilla, Fabric or Forge: dimensions/minecraft/overworld/region, dimensions/minecraft/the_nether/region and dimensions/minecraft/the_end/region. All three dimensions sit inside world.
• Minecraft 26.1 and later on Paper or Purpur: the same three folders inside world, because Paper 26.1 moved its dimensions to the Vanilla layout and Purpur is built on Paper.
• Before 26.1 on Vanilla, Fabric or Forge: region, DIM-1/region and DIM1/region.
• Before 26.1 on Paper, or Purpur which is built on it: region in world, DIM-1/region in world_nether and DIM1/region in world_the_end.

This list does not cover NeoForge, Quilt or Folia. If you run one of those, or you cannot see the folders listed for your version, open world and look at what is there before you change anything.

Folders named entities and poi sit beside region and use the same file names. If the log names one of them, work in that folder instead.

Fix 1: restore a backup

This is the simplest repair and it covers everything at once. Restoring replaces your files with the backup's, so you lose progress made since. See How to create and restore backups.

Fix 2: replace only the damaged file

This keeps everything else exactly as it is.

1. Press Stop on the Console tab and wait for the server to stop.
2. On the Backups tab, press Download on a backup from before the damage.
3. Unpack the .tar.gz on your computer and find the same r.X.Z.mca at the same path. A backup holds every file unless you listed the world folder in the Ignored files/folders box of the create form when you made it.
4. In the File Manager, Rename the damaged file to r.X.Z.mca.bad, so you still have it.
5. Press Upload and send the good file. Browser uploads stop at 100 MB per file, so use SFTP for anything bigger: Connect over SFTP with FileZilla or WinSCP.
6. Start the server and watch the Console for the same message.

Everything stored in that area goes back to how it was on the backup's date.

Fix 3: remove the file and let the game rebuild it

Use this only when no backup is usable.

1. Stop the server.
2. Rename the damaged file to r.X.Z.mca.bad.
3. Start the server and walk to the area. New terrain generates as players arrive.

Keep the .bad file until you are sure you do not want it. minecraft.wiki also lists a community command-line tool, Minecraft Region Fixer, for repairing region files on a downloaded copy. Check it supports your game version first.

Stop it happening again

• Use Stop, not Force stop. The panel warns that Force stop skips the graceful shutdown, so anything unsaved can be lost.
• Keep an eye on the disk. A full disk breaks saves: Server out of disk space? Free it up.
• On Vanilla, Fabric, Forge and NeoForge, switch on Sync chunk writes in the Config Editor under Performance. minecraft.wiki says it prevents data loss and corruption after a crash, at the cost of speed. Our installer sets it to off, so check it again after a reinstall. On Paper the setting has no effect: the Paper documentation says it only works there when a system property is also set, and you cannot set Java system properties on our servers. Purpur is built on top of Paper, so do not rely on the setting there either.
• A server killed for using too much memory can die mid-save: Minecraft server exit codes 1, 137 and 143.
• Schedule backups so there is always a recent one: How to create and restore backups.