I go at my chest freezer hammer-and-tongs, with bowls of hot water and that thingy which I use for getting frost off the car windscreen. I go mad, furiously hacking at the ice, and get it all off in about ten/fifteen minutes. The freezer hardly has time to warm up, so I wipe it dry, turn it back on, and pile back into it all the ice-packs and icecubes, while I clean and sterilise all the baskets. When that's all done, the freezer is cold enough to put the food back. ( I get the food stocks as low as possible, and transfer stuff to another freezer) Whole job done in under an hour and it's not a particularly small freezer. Such a relief to get it over with, after all that frenzied effort !