Chapter 20. The Z File System (ZFS)

Written by Tom Rhodes, Allan Jude, Benedict Reuschling and Warren Block.
Table of Contents
20.1. What Makes ZFS Different
20.2. Quick Start Guide
20.3. zpool Administration
20.4. zfs Administration
20.5. Delegated Administration
20.6. ZFS Advanced Topics
20.7. Additional Resources
20.8. ZFS Features and Terminology

The Z File System, or ZFS, is an advanced file system designed to overcome many of the major problems found in previous designs.

Originally developed at Sun™, ongoing ZFS development has moved to the OpenZFS Project. Section 20.7.1, “History of ZFS describes the development history in more detail.

ZFS has three major design goals:

A complete list of features and terminology is shown in Section 20.8, “ZFS Features and Terminology”.

20.1. What Makes ZFS Different

ZFS is significantly different from any previous file system because it is more than just a file system. Combining the traditionally separate roles of volume manager and file system provides ZFS with unique advantages. The file system is now aware of the underlying structure of the disks. Traditional file systems could only be created on a single disk at a time. If there were two disks then two separate file systems would have to be created. In a traditional hardware RAID configuration, this problem was worked around by presenting the operating system with a single logical disk made up of the space provided by a number of disks, on top of which the operating system placed its file system. Even in the case of software RAID solutions like GEOM, the UFS file system living on top of the RAID transform believed that it was dealing with a single device. ZFS's combination of the volume manager and the file system solves this and allows the creation of many file systems all sharing a pool of available storage. One of the biggest advantages to ZFS's awareness of the physical layout of the disks is that ZFS can grow the existing file systems automatically when additional disks are added to the pool. This new space is then made available to all of the file systems. ZFS also has a number of different properties that can be applied to each file system, creating many advantages to creating a number of different filesystems and datasets rather than a single monolithic filesystem.

All FreeBSD documents are available for download at

Questions that are not answered by the documentation may be sent to <>.
Send questions about this document to <>.