java.lang.RuntimeException: Failed to migrate world storage for world_nether - with latest version 26.1.2 #60

[ttys42]

Stack trace

[17:36:48 ERROR]: Encountered an unexpected exception
java.lang.RuntimeException: Failed to migrate world storage for world_nether
        at io.papermc.paper.world.PaperWorldLoader.getWorldInfoAndData(PaperWorldLoader.java:65) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.PaperWorldLoader.loadInitialWorld(PaperWorldLoader.java:150) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.PaperWorldLoader.loadInitialWorlds(PaperWorldLoader.java:139) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at net.minecraft.server.MinecraftServer.loadLevel(MinecraftServer.java:650) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:382) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1301) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:304) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at java.base/java.lang.Thread.run(Thread.java:1474) ~[?:?]
Caused by: java.io.IOException: Refusing to overwrite existing migrated file ./world/dimensions/minecraft/the_nether/region/r.0.-1.mca while moving ./world_nether/DIM-1/region/r.0.-1.mca
        at io.papermc.paper.world.migration.WorldMigrationSupport.mergeMove(WorldMigrationSupport.java:116) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.migration.WorldMigrationSupport.mergeMove(WorldMigrationSupport.java:108) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.migration.WorldMigrationSupport.migrateDimensionDirectories(WorldMigrationSupport.java:99) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.migration.LegacyCraftBukkitWorldMigration.run(LegacyCraftBukkitWorldMigration.java:82) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.migration.LegacyCraftBukkitWorldMigration.migrate(LegacyCraftBukkitWorldMigration.java:52) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.migration.WorldFolderMigration.migrateStartupWorld(WorldFolderMigration.java:48) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        at io.papermc.paper.world.PaperWorldLoader.getWorldInfoAndData(PaperWorldLoader.java:63) ~[paper-26.1.2.jar:26.1.2-60-b4682bf]
        ... 7 more

Plugin and Datapack List

Geyser-Spigot.jar - Build 1137

Actions to reproduce (if known)

Start the world with the new version.

Paper version

26.1.2-60

Other

The world runs fine with paper 1.21.11-130.jar but cannot be migrated to the latest version 26.1.2-60.

I have the stack trace that is shown at startup pasted and also added the crash log.

crash-2026-05-07_17.36.48-server.txt

[mbax]

At some point you had a vanilla world you migrated to Paper, and ended up with a spare DIM-1 folder in the nether folder. Restore your backup, delete the DIM-1 folder inside the world_nether folder, and try again. (Keep the backup, obviously, don't delete that or delete the DIM-1 from it, just in case).

Regardless, Paper should probably catch this fairly common issue and give users the opportunity to correct the issue in advance or auto-back up that DIM folder.

[ttys42]

Confirming a successful migration after reverting the backup and deleting the DIM-1 folder.
If this is a common issue, I agree paper should ideally catch this while upgrading to improve user experience.

Will leave this issue open if needed to track this otherwise this issue can be seen as resolved.

[Doc94]

Thanks @ttys42 for the check.

Im going to close this how duplicated of #13863 but exists a PR #13872 for improvement the error message and make more clear this issue its related to other dimension already migrate the same DIM folder. because based in how vanilla works with the dimension not exists an easy way to check this before all the migration start.