Concatenated Metadevice (Concatenation)

A concatenated metadevice, or concatenation, is a metadevice whose data is organized serially and adjacently across disk slices, forming one logical storage unit.

You would use a concatenated metadevice to get more storage capacity by logically combining the capacities of several slices. You can add more slices to the concatenated metadevice as the demand for storage grows.

A concatenated metadevice enables you to dynamically expand storage capacity and file system sizes online. With a concatenated metadevice you can add slices even if the other slices are currently active.

To increase the capacity of a striped metadevice, you would have to build a concatenated stripe (see "Concatenated Stripe").

A concatenated metadevice can also expand any active and mounted UFS file system without having to bring down the system. In general, the total capacity of a concatenated metadevice is equal to the total size of all the slices in the concatenated metadevice. If a concatenation contains a slice with a state database replica, the total capacity of the concatenation would be the sum of the slices less the space reserved for the replica.

You can also create a concatenated metadevice from a single slice. You could, for example, create a single-slice concatenated metadevice. Later, when you need more storage, you can add more slices to the concatenated metadevice.

Concatenations have names like other metadevices (d0, d1, and so forth). For more information on metadevice naming, see Table 1-4.