Buggy obsidian making : MineCraft

I dunno how many people know about this. A friend told me about this bug that is apparently illegal if youre caught on his server but I don't know about others. You put down some redstone in a line, and build a wall on either side so it's like a corridor. Build a pull of water on one side and knock out the bottom blocks on the flowing water is touching the redstone. Build a lava pit at the head of the corridor and slightly higher (2-3 blocks, acting like a ramp) with the lava held back by a piston. When you open the piston, the lava should flow down onto the redstone and covert it into obsidian. Close the piston to stop the lava flow and you're ready to mine it.