Minecraft wiki entry for Mob_farm, associated text: 1 Locations
2 Drops
3 Designs
3.1 Spawning tower
3.1.1 Using observer blocks
3.2 Sinkhole
3.3 Canal-style
3.3.1 Compact canal design
3.3.2 Minimal canal design
3.3.3 Large chamber fully automatic design
3.3.4 Water pans
3.4 Active mob displacement
3.5 Other designs
4 Transporting mobs
4.1 Horizontal transportation
4.2 Downward transportation
4.3 Upward transportation
5 Grinding
6 Video
7 Performance concerns