But why ZFS?
FreeNAS uses ZFS because it is an enterprise-ready open source file system and volume manager with unprecedented flexibility and an uncompromising commitment to data integrity. ZFS is a truly next-generation file system that eliminates most, if not all of the shortcomings found in legacy file systems and hardware RAID devices. Once you go ZFS, you will never want to go back.
ZFS helps you avoid most storage planning mistakes by pooling together the blocks provided by all of your disks and allowing you to divide the available space into highly-configurable file systems. ZFS includes the permissions and quotas of traditional file systems but also includes transparent compression levels, capacity reservations, and clonable snapshots. Of these features, snapshots will probably be the one that forever changes the way you think about storage. Imagine if you could bring “what if?” style experimentation to your storage.
Uncompromising Data Integrity
Unprecedented flexibility is pointless without dependability. ZFS is uncompromising about data integrity and data redundancy. ZFS creates a chain of trust for your data by checksumming data when it is written and verifying the checksums when it is read. It even checksums the metadata that describes the file system and allows you to periodically verify all checksums to determine if your infrequently-used data or backups are suffering silent data corruption a.k.a. “bit rot”. By taking these precautions, ZFS will never return you corrupt data from disk.
Knowing your data is intact is one thing but combating disk unreliability is quite another. ZFS can maintain data redundancy through a sophisticated system of multiple disk strategies. These strategies include mirroring and the striping of mirrors equvalent to traditional RAID 1 and 10 arrays but also includes “RaidZ” configurations that tolerate the failure of one, two or three member disks of a given set of member disks.