Logical volumes

Understand how logical volumes can be exported to client partitions as virtual SCSI disks. A logical volume is a portion of a physical volume.

A hierarchy of structures is used to manage disk storage. Each individual disk drive or LUN, called a physical volume, has a name, such as /dev/hdisk0. Every physical volume in use either belongs to a volume group or is used directly for virtual storage. All of the physical volumes in a volume group are divided into physical partitions of the same size. The number of physical partitions in each region varies, depending on the total capacity of the disk drive.

Within each volume group, one or more logical volumes are defined. Logical volumes are groups of information located on physical volumes. Data on logical volumes appears to the user to be contiguous but can be discontiguous on the physical volume. This allows logical volumes to be resized or relocated and to have their contents replicated.

Each logical volume consists of one or more logical partitions. Each logical partition corresponds to at least one physical partition. Although the logical partitions are numbered consecutively, the underlying physical partitions are not necessarily consecutive or contiguous.

After installation, the system has one volume group (the rootvg volume group) consisting of a base set of logical volumes required to start the system.

You can use the commands described in the following table to manage logical volumes.

Table 1. Logical volume commands and their descriptions
Logical volume command	Description
chlv	Changes the characteristics of a logical volume.
cplv	Copies the contents of a logical volume to a new logical volume.
extendlv	Increases the size of a logical volume.
lslv	Displays information about the logical volume.
mklv	Creates a logical volume.
mklvcopy	Creates a copy of a logical volume.
rmlv	Removes logical volumes from a volume group.
rmlvcopy	Removes a copy of a logical volume.

Creating one or more distinct volume groups rather than using logical volumes that are created in the rootvg volume group allows you to install any newer versions of the Virtual I/O Server while maintaining client data by exporting and importing the volume groups created for virtual I/O.

Notes:

Logical volumes used as virtual disks must be less than 1 TB (where TB equals 1 099 511 627 776 bytes) in size.
For best performance, avoid using logical volumes (on the Virtual I/O Server) as virtual disks that are mirrored or striped across multiple physical volumes.