Jump to content United States-English
HP.com Home Products and Services Support and Drivers Solutions How to Buy
» Contact HP
More options
HP.com home
HP-UX System Administrator's Guide: Logical Volume Management: HP-UX 11i Version 3 > Chapter 1 Introduction

LVM Architecture


Technical documentation

Complete book in PDF
» Feedback
Content starts here

 » Table of Contents

 » Glossary

 » Index

An LVM system starts by initializing disks for LVM usage. An LVM disk is known as a physical volume (PV). A disk is marked as an LVM physical volume using either the HP System Management Homepage (HP SMH) or the pvcreate command. Physical volumes use the same device special files as traditional HP-UX disk devices.

LVM divides each physical volume into addressable units called physical extents (PEs). Starting after the LVM metadata at the beginning of the disk, extents are allocated sequentially, with an index starting at zero and incrementing by one for each unit. The physical extent size is configurable at the time you form a volume group and applies to all disks in the volume group. You can select a size from 1 MB to 256 MB.

Physical volumes are organized into volume groups (VGs). A volume group can consist of one or more physical volumes, and there can be more than one volume group in the system. Once created, the volume group, not the disk, is the entity that represents data storage. Thus, whereas earlier you moved disks from one system to another, with LVM, you move a volume group from one system to another. Therefore, it is often convenient to have multiple volume groups on a system.

The pool of disk space that is represented by a volume group can be divided into logical volumes (LVs) of various sizes. Once created, logical volumes can be treated just like disk partitions. They are accessible through device special files. A logical volume can span a number of physical volumes in a volume group or represent only part of one physical volume.

The basic allocation units for a logical volume are called logical extents (LEs). A logical extent is mapped to a physical extent. Thus, if the physical extent size is 4 MB, the logical extent size is also 4 MB. The size of a logical volume is determined by the number of logical extents configured.

You assign file systems, swap, dump, or raw data to logical volumes. For example, in Figure 1-1, logical volume /dev/vg01/lvol1 might contain a file system, logical volume /dev/vg01/lvol2 might contain swap space, and logical volume /dev/vg01/lvol3 might contain raw data. You can use HP SMH to create a file system in a logical volume of a specified size, then mount the file system. Alternately, you can use LVM commands to create, then extend a logical volume to allocate sufficient space for file systems or raw data. You then create and mount new file systems or install your application in the logical volume.

Figure 1-1 Disk Space Partitioned Into Logical Volumes

Space Partitioned Into Logical Volumes
Printable version
Privacy statement Using this site means you accept its terms Feedback to webmaster
© 2008 Hewlett-Packard Development Company, L.P.