Minecraft wiki entry for Server_level.dat, associated text: The server level.dat file is where the Minecraft Server dumps the level information for permanent storage. As this file is primarily raw level data, it can be quite large: a regular 256×256×64 sized level is 4 megabytes in size. The file is compressed using gzip, however. Most of the block values are 0 (empty space), so, therefore, the size is reduced considerably by the compression, usually down to a few hundred kilobytes.