btrfs-tools 4.0-2 (amd64 binary) in ubuntu wily

 Btrfs is a new copy on write filesystem for Linux aimed at implementing
 advanced features while focusing on fault tolerance, repair and easy
 administration.
 .
 This package contains utilities (mkfs, fsck) used to work with btrfs
 and an utility (btrfs-convert) to make a btrfs filesystem from an ext3.