btrfs-tools 0.19+20100601-3ubuntu2 (amd64 binary) in ubuntu oneiric

 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, btrfsctl) used to work with btrfs
 and an utility (btrfs-convert) to make a btrfs filesystem from an ext3.
 .
 WARNING: Btrfs is under heavy development, and is not suitable for any uses
 other than benchmarking and review.