ZFS is an emerging file system developed at Sun Microsystems.
Unlike traditional file systems like FAT32 or NTFS, which you would find on a Windows-based system, ZFS can “pool” multiple disks together so they appear as a single volume to the user. This is similar to a RAID configuration, but implemented in the file system rather than above it.
Another thing that ZFS implements is copy-on-write, which means that whenever a piece of data on the disk is changed, the new version does not overwrite the old version. This enables the system to take “snapshots” of the disk at any point in time, since virtually every iteration of the stored data is available. Snapshots can be used to easily clone a copy of the entire file system from a specific date and time. ZFS has been open sourced by Sun and is currently being deployed on FreeBSD, Mac OS X, and Solaris.