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HP-UX System Administrator's Guide: Logical Volume Management: HP-UX 11i Version 3 > Chapter 1 Introduction

LVM Features


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Logical Volume Manager (LVM) is a storage management system that lets you allocate and manage disk space for file systems or raw data. Historically, you treated your disks individually and in terms of fixed-sized partitions; each disk or partition held a file system, swap space, boot area, or raw data. With LVM, you do not need to assign a disk or fixed-sized partition to a single purpose. Instead, consider the disks as a pool (or volume) of data storage, consisting of equal-sized extents. Extents are allocated into virtual storage devices known as logical volumes, which can be treated as disks.

LVM provides the following capabilities:

  • A logical volume size can be dynamically reduced or expanded to meet changing data needs. For example, a logical volume can be as small or large as the file system mounted to it requires. The file system can be extended without rebuilding it or the logical volume; reducing a file system is more complex, and may require recreating the file system.

  • Small chunks of unused space from several disks can be combined to create a usable volume.

  • A logical volume can exceed the size of a single physical disk. This feature is called disk spanning, because a single file system (and individual files) can span disks.

  • Up to six copies of identical data can be stored and updated simultaneously using LVM. This feature is called mirroring a logical volume, and requires an optional product, HP MirrorDisk/UX. See “Increasing Data Availability Through Mirroring”.

  • Mirrored data can be configured to automatically create a new mirror to a separate disk when one of the mirror copies fails. This feature is called sparing, and requires an optional product, HP MirrorDisk/UX. See “Increasing Disk Redundancy Through Disk Sparing”.

  • A logical volume can be created so that logically contiguous data blocks (for example, chunks of the same file) are distributed across multiple disks, which speeds I/O throughput for large files when they are read and written sequentially. This feature is called striping. Striping can be used in conjunction with mirroring. See “Increasing Performance Through Disk Striping”.

  • Devices accessed through multiple links can be configured to improve availability. If the primary link to a device fails, LVM can switch automatically to an alternate link. This feature is called multipathing. See “Increasing Hardware Path Redundancy Through Multipathing”.

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