ZFS is a member of the newer generation of filesystems that include advanced features beyond simple file storage. Its capabilities are quite extensive covering a wide range of pain points hit with previous filesystems. The Wikipedia page details them all nicely but for the purpose of this post we will be focusing on its ability to create N-Way sets of disk mirrors.
Traditionally mirrored disk sets in Linux and other operating systems have been limited to two devices (note: devices in this context could be disks, partitions or even other raid groups, such is the case in raid 10 setups). While mirroring has the benefit over other raid levels in that each mirrored device contains a complete copy of the data, the two device limit became inadequate as disk sizes ballooned. In the age of multi-TB drives, simply rebuilding a degraded mirrored array could actually cause the surviving device to fail, eliminating the very redundancy one was expecting.
ZFS addresses this particular problem in several ways through data checksums, self-healing and smart resilveringinstead of blindly rebuilding full array members even if only 1% of disk space is being used.
Read more at http://www.bhoey.com/blog/.