The Lvm Logical Volume Manager; Logical Volumes - Red Hat ENTERPRISE LINUX 5.1 - LVM ADMINISTRATION Manual

Chapter 1.

The LVM Logical Volume Manager

This chapter provides a high-level overview of the components of the Logical Volume Manager (LVM).

1.1. Logical Volumes

Volume management creates a layer of abstraction over physical storage, allowing you to create
logical storage volumes. This provides much greater flexibility in a number of ways than using physical
storage directly.
A logical volume provides storage virtualization. With a logical volume, you are not restricted to
physical disk sizes. In addition, the hardware storage configuration is hidden from the software so it
can be resized and moved without stopping applications or unmounting file systems. This can reduce
operational costs.
Logical volumes provide the following advantages over using physical storage directly:
• Flexible capacity
When using logical volumes, file systems can extend across multiple disks, since you can aggregate
disks and partitions into a single logical volume.
• Resizeable storage pools
You can extend logical volumes or reduce logical volumes in size with simple software commands,
without reformatting and repartitioning the underlying disk devices.
• Online data relocation
To deploy newer, faster, or more resilient storage subsystems, you can move data while your system
is active. Data can be rearranged on disks while the disks are in use. For example, you can empty a
hot-swappable disk before removing it.
• Convenient device naming
Logical storage volumes can be managed in user-defined groups, which you can name according to
your convenience.
• Disk striping
You can create a logical volume that stripes data across two or more disks. This can dramatically
increase throughput.
• Mirroring volumes
Logical volumes provide a convenient way to configure a mirror for your data.
• Volume Snapshots
Using logical volumes, you can take device snapshots for consistent backups or to test the effect of
changes without affecting the real data.
The implementation of these features in LVM is described in the remainder of this document.
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