Installation guide

LVM Architecture Overview

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. 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.

1.3. LVM Architecture Overview

For the Red Hat Enterprise Linux 4 release of the Linux operating system, the original LVM1 logical

volume manager was replaced by LVM2, which has a more generic kernel framework than LVM1.

LVM2 provides the following improvements over LVM1:

• flexible capacity

• more efficient metadata storage

• better recovery format

• new ASCII metadata format