Solaris Volume Manager Administration Guide

Overview of Solaris Volume Manager Components

The four basic types of components that you create with Solaris Volume Manager are volumes, disk sets, state database replicas, and hot spare pools. The following table gives an overview of these Solaris Volume Manager components.

Table 3–1 Summary of Solaris Volume Manager Components

Solaris Volume Manager Component 



For More Information 

RAID 0 volumes (stripe, concatenation, concatenated stripe), RAID 1 (mirror) volumes, RAID 5 volumes

A group of physical slices that appear to the system as a single, logical device 

To increase storage capacity, performance, or data availability. 


Soft partitions 

Subdivisions of physical slices or logical volumes to provide smaller, more manageable storage units 

To improve manageability of large storage volumes.  


State database (state database replicas)

A database that stores information on disk about the state of your Solaris Volume Manager configuration 

Solaris Volume Manager cannot operate until you have created the state database replicas. 

State Database and State Database Replicas

Hot spare pool

A collection of slices (hot spares) reserved to be automatically substituted in case of component failure in either a submirror or RAID 5 volume 

To increase data availability for RAID 1 and RAID 5 volumes. 

Hot Spare Pools

Disk set

A set of shared disk drives in a separate namespace that contain volumes and hot spares and that can be non-concurrently shared by multiple hosts 

To provide data redundancy and availability and to provide a separate namespace for easier administration. 

Disk Sets


A volume is a name for a group of physical slices that appear to the system as a single, logical device. Volumes are actually pseudo, or virtual, devices in standard UNIX® terms.

Note –

Historically, the Solstice DiskSuiteTM product referred to these as “metadevices.” However, for simplicity and standardization, this book refers to them as “volumes.”

Classes of Volumes

You create a volume as a RAID 0 (concatenation or stripe) volume, a RAID 1 (mirror) volume, a RAID 5 volume, a soft partition, or a UFS logging volume.

You can use either the Enhanced Storage tool within the Solaris Management Console or the command-line utilities to create and administer volumes.

The following table summarizes the classes of volumes:

Table 3–2 Classes of Volumes



RAID 0 (stripe or concatenation)

Can be used directly, or as the basic building blocks for mirrors and transactional devices. By themselves, RAID 0 volumes do not provide data redundancy.  

RAID 1 (mirror)

Replicates data by maintaining multiple copies. A RAID 1 volume is composed of one or more RAID 0 volumes called submirrors. 


Replicates data by using parity information. In the case of disk failure, the missing data can be regenerated by using available data and the parity information. A RAID 5 volume is generally 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. 


Used to log a UFS file system. (UFS logging is a preferable solution to this need, however.) 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 RAID5 volume. The master device contains the UFS file system. 

Soft partition 

Divides a slice or logical volume into one or more smaller, extensible volumes. 

How Are Volumes Used?

You use volumes to increase storage capacity, performance, 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 Names for details about volume names.

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

Example—Volume That Consists of Two Slices

Figure 3–2 shows a volume “containing” two slices, one each from Disk A and Disk B. An application or UFS will treat the volume as if it were one physical disk. Adding more slices to the volume will increase its capacity.

Figure 3–2 Relationship Among a Volume, Physical Disks, and Slices


Volume and Disk Space Expansion

Solaris Volume Manager enables you to expand a volume by adding additional slices. You can use either the Enhanced Storage tool within the Solaris Management Console or the command line interface to add a slice to an existing volume.

You can expand a mounted or unmounted UFS file system that is contained within a volume without having to halt or back up your system. (Nevertheless, backing up your data is always a good idea.) After you expand the volume, use the growfs command to grow the file system.

Note –

After a file system has been expanded, it cannot be shrunk. Not shrinking the size of a file system is a UFS limitation. Similarly, after a Solaris Volume Manager partition has been increased in size, it cannot be reduced.

Applications and databases that use the raw volume must have their own method to “grow” the added space so that the application or database can recognize it. Solaris Volume Manager does not provide this capability.

You can expand the disk space in volumes in the following ways:

The growfs Command

The growfs command expands a UFS file system without loss of service or data. However, write access to the volume is suspended while the growfs command is running. You can expand the file system to the size of the slice or the volume that contains the file system.

The file system can be expanded to use only part of the additional disk space by using the -s size option to the growfs command.

Note –

When you expand a mirror, space is added to the mirror's underlying submirrors. Likewise, when you expand a transactional volume, space is added to the master device. The growfs command is then run on the RAID 1 volume or the transactional volume, respectively. The general rule is that space is added to the underlying devices, and the growfs command is run on the top-level device.

Volume Names

Volume Name Requirements

There are a few rules that you must follow when assigning names for volumes:

Volume Name Guidelines

The use of a standard for your volume names can simplify administration, and enable you at a glance to identify the volume type. Here are a few suggestions:

State Database and State Database Replicas

The state database is a database that stores information on disk about the state of your Solaris Volume Manager configuration. The state database records and tracks changes made to your configuration. Solaris Volume Manager automatically updates the state database when a configuration or state change occurs. Creating a new volume is an example of a configuration change. A submirror failure is an example of a state change.

The state database is actually a collection of multiple, replicated database copies. Each copy, referred to as a state database replica, ensures that the data in the database is always valid. Having copies of the state database protects against data loss from single points-of-failure. The state database tracks the location and status of all known state database replicas.

Solaris Volume Manager cannot operate until you have created the state database and its state database replicas. It is necessary that a Solaris Volume Manager configuration have an operating state database.

When you set up your configuration, you can locate the state database replicas on either of the following:

Solaris Volume Manager recognizes when a slice contains a state database replica, and automatically skips over the portion of the slice reserved for the replica if the slice is used in a volume. The part of a slice reserved for the state database replica should not be used for any other purpose.

You can keep more than one copy of a state database on one slice. However, you might make the system more vulnerable to a single point-of-failure by doing so.

The system will continue to function correctly if all state database replicas are deleted. However, the system will lose all Solaris Volume Manager configuration data if a reboot occurs with no existing state database replicas on disk.

Hot Spare Pools

A hot spare pool is a collection of slices (hot spares) reserved by Solaris Volume Manager to be automatically substituted in case of a slice failure in either a submirror or RAID 5 volume. Hot spares provide increased data availability for RAID 1 and RAID 5 volumes. You can create a hot spare pool with either the Enhanced Storage tool within the Solaris Management Console or the command line interface.

When errors occur, Solaris Volume Manager checks the hot spare pool for the first available hot spare whose size is equal to or greater than the size of the slice being replaced. If found, Solaris Volume Manager automatically resynchronizes the data. If a slice of adequate size is not found in the list of hot spares, the submirror or RAID 5 volume is considered to have failed. For more information, see Chapter 15, Hot Spare Pools (Overview).

Disk Sets

A shared disk set, or simply disk set, is a set of disk drives that contain state database replicas, volumes, and hot spares that can be shared exclusively but not at the same time by multiple hosts.

A disk set provides for data availability in a clustered environment. If one host fails, another host can take over the failed host's disk set. (This type of configuration is known as a failover configuration.) Additionally, disk sets can be used to help manage the Solaris Volume Manager name space, and to provide ready access to network-attached storage devices.

For more information, see Chapter 19, Disk Sets (Overview).