The February 2012 issue of ;login: has a detailed overview of Btrfs [PDF] written by developer Josef Bacik. “Btrfs’s snapshotting is simple to use and understand. The snapshots will show up as normal directories under the snapshotted directory, and you can cd into it and walk around like in a normal directory. By default, all snapshots are writeable in Btrfs, but you can create read-only snapshots if you so choose. Read-only snapshots are great if you are just going to take a snapshot for a backup and then delete it once the backup completes. Writeable snapshots are handy because you can do things such as snapshot your file system before performing a system update; if the update breaks your system, you can reboot into the snapshot and use it like your normal file system.”