I am experimenting with BTRFS on a home server and very newbish to BTRFS. I have been reviewing btrfs wiki and Wikipedia CoW. Bottom line, I have a 40GB SATA Hard Drive and I am out of space. The free space scheme is very complicated to me on BTRFS at first glance and whether or not disabling CoW would be an advantage? What is the purpose of CoW? I had assumed that it would make a copy of changed blocks for later retrieval?