Volumes

A volume or logical volume is a name for a group of physical slices that appear to the system as a single device. You might know the concept of volumes as "metadevices", in Solstice Disk Suite terminology, or as pseudo or virtual devices in standard UNIX terms.

How Are Volumes Used?

You use volumes to increase storage capacity and data availability. In some instances, volumes can also increase I/O performance. Functionally, volumes behave the same way as slices. Because volumes look like slices, they are transparent to end users, applications, and file systems. Like physical devices, volumes are accessed through block or raw device names. The volume name changes, depending on whether the block or raw device is used. See Volume Conventions for details about volume names.

You can use most file systems commands (mount(1M), umount(1M), ufsdump(1M), ufsrestore(1M), and so forth) on volumes. You cannot use the format(1M) command, however. You can read, write, and copy files to and from a volume, as long as you have a file system mounted on the volume.

The following table summarizes the types of logical volumes:

Types of Volumes

Volume

Description

RAID 0 (Stripes and Concatenations)

Can be used directly, or as the basic building blocks for RAID 1 volumes (mirrors) and transactional volumes. All three types of simple volumes--stripes, concatenations, and concatenated stripes-- consist only of physical slices. Simple volumes expand storage capacity for a single file system, but do not provide data redundancy.

RAID 1 (Mirror)

Replicates data by maintaining multiple copies. A mirror is composed of one or more RAID 0 volumes called submirrors.

RAID 5

Replicates data by using parity information. In the case of missing data, the missing data can be regenerated using available data and the parity information. A RAID 5 volume is composed of slices. One slice's worth of space is allocated to parity information, but it is distributed across all slices in the RAID 5 volume.

Transactional volumes

Logs a file system, like UFS logging. A transactional volume is composed of a master device and a logging device. Both of these devices can be a slice, RAID 0 volume, RAID 1 volume, or RAID 5 volume. The master device contains the logged file system.

Soft partition volumes

Divides a disk into as many divisions as needed. These divisions can then be accessed by applications, including file systems. Soft partitions can be placed directly above a disk slice, or on top of a mirror, stripe, or RAID 5 volume.