ZFS Terminology

This section describes the basic terminology used throughout this book:

alternate boot environment

A boot environment that is created by the lucreate command and possibly updated by the luupgrade command, but it is not currently the active or primary boot environment. The alternate boot environment (ABE) can be changed to the primary boot environment (PBE) by running the luactivate command.

checksum

A 256-bit hash of the data in a file system block. The checksum capability can range from the simple and fast fletcher4 (the default) to cryptographically strong hashes such as SHA256.

clone

A file system whose initial contents are identical to the contents of a snapshot.

For information about clones, see Overview of ZFS Clones.

dataset

A generic name for the following ZFS entities: clones, file systems, snapshots, or volumes.

Each dataset is identified by a unique name in the ZFS namespace. Datasets are identified using the following format:

pool/path[@snapshot]

pool

Identifies the name of the storage pool that contains the dataset

path

Is a slash-delimited path name for the dataset object

snapshot

Is an optional component that identifies a snapshot of a dataset

For more information about datasets, see Chapter 6, Managing ZFS File Systems.

file system

A ZFS dataset of type filesystem that is mounted within the standard system namespace and behaves like other file systems.

For more information about file systems, see Chapter 6, Managing ZFS File Systems.

mirror

A virtual device that stores identical copies of data on two or more disks. If any disk in a mirror fails, any other disk in that mirror can provide the same data.

pool

A logical group of devices describing the layout and physical characteristics of the available storage. Space for datasets is allocated from a pool.

For more information about storage pools, see Chapter 4, Managing ZFS Storage Pools.

primary boot environment

A boot environment that is used by the lucreate command to build the alternate boot environment. By default, the primary boot environment (PBE) is the current boot environment. This default can be overridden by using the lucreate -s option.

RAID-Z

A virtual device that stores data and parity on multiple disks. For more information about RAID-Z, see RAID-Z Storage Pool Configuration.

resilvering

The process of transferring data from one device to another device is known as resilvering. For example, if a mirror component is replaced or taken offline, the data from the up-to-date mirror component is copied to the newly restored mirror component. This process is referred to as mirror resynchronization in traditional volume management products.

For more information about ZFS resilvering, see Viewing Resilvering Status.

snapshot

A read-only image of a file system or volume at a given point in time.

For more information about snapshots, see Overview of ZFS Snapshots.

virtual device

A logical device in a pool, which can be a physical device, a file, or a collection of devices.

For more information about virtual devices, see Displaying Storage Pool Virtual Device Information.

volume

A dataset used to emulate a physical device. For example, you can create a ZFS volume as a swap device.

For more information about ZFS volumes, see ZFS Volumes.