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What to do when the world is corrupt

Symptoms, the causes behind them, and the order of things to try before you reach for a backup.

1 min readUpdated 2026-09-14Diese Anleitung auf Deutsch lesen →

How it shows

  • The server crashes when a player enters a certain area; the log mentions region, chunk, .mca or Failed to load level.dat.
  • Chunks look reset or missing.
  • The server hangs on Loading level forever.

Why it happens

Almost always an unclean shutdown: the process was killed while writing (the Kill button, running out of RAM, a disk that was full). Rarely a buggy mod or plugin that writes garbage.

In this order

  1. Stop the server cleanly. Do not keep restarting, because every start on a broken world can make it worse.
  2. Back up now (Backups → Create). Even a broken world is better than none while you work.
  3. level.dat broken? Rename world/level.dat_old to level.dat. Minecraft keeps the previous copy.
  4. A single chunk? Note the coordinates from the log, delete the region file that contains them (world/region/r.X.Z.mca, where X = blockX ÷ 512 rounded down, Z likewise). That area regenerates empty; everything else stays.
  5. Still broken? Restore the newest backup, or only the world if the rest of the server is fine.
  6. No backup? Kowalski can try the region-file route for you and tell you what is lost. Beyond that, tools like MCA Selector on your PC can repair individual chunks, but that is a rabbit hole.

Prevent it

Use Stop instead of Kill, keep the disk from filling up, give modpacks enough RAM, and let a schedule take a backup every night.