If the given information by Mojang is true, you CAN exceed the 128-block-limit right? https://mojang.com/2012/02/new-minecraft-map-format-anvil/ Spoiler: If you don't like clicking links NEW MINECRAFT MAP FORMAT, "ANVIL" Posted on Feb 14, 2012 by Jens Bergensten Hello! Jon and I have been working on a new map format for Minecraft that we’ve dubbed “Anvil” (it’s just a name). The purpose of the new format is to prepare for modding, especially to allow for more block types, but also to improve other areas of the game (such as map height). The changes are: Maximum build height has been increased to 256 (was 128) Empty sections of the world are not loaded into memory Block ids have been increased to 4096 (was 256) by adding a 4 bit data layer (similar to how meta data is stored) Block ordering have been changed from x/z/y to y/z/x in order to improve compression Packets for sending chunks have been updated (a full 128-high chunk is smaller than the old format, and a chunk with lots of empty space is much smaller) Biomes are saved per x/z column, which means they can be altered by tools The next snapshot, and Minecraft 1.2, will automatically convert worlds to the new format. The files of the current format (“McRegion”) will remain in your save folder, if you need to restore them for some reason.