FileSystem > Btrfs
Btrfs is intended to address the lack of pooling, snapshots, checksums, and integral multi-device spanning in Linux file systems, these features being crucial as the use of Linux scales upward into larger storage configurations. Btrfs is designed to be a multipurpose filesystem, scaling well on very large block devices.
Even though Btrfs has been in the kernel since 2.6.29, the developers state that "as of 2.6.31, we only plan to make forward compatible disk format changes". The developers still want to improve the user/management tools to make them easier to use. For more information about Btrfs, follow the links in See also section.
Ext2/3/4 filesystems should be upgradable to Btrfs (but not the other way around).
DebianSqueeze and later support Btrfs.
See also: Btrfs wiki FAQ
/usr/share/doc/linux-doc-2.6.*/Documentation/filesystems/btrfs.txt.gz, also available online for 2.6.32
Btrfs wiki: https://btrfs.wiki.kernel.org/
Btrfs on Wikipedia