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Chapter 1. Overview of logical volume management

Logical volume management (LVM) creates a layer of abstraction over physical storage, which helps you to create logical storage volumes. This provides much greater flexibility in a number of ways than using physical storage directly.

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.

1.1. LVM architecture

The following are the components of LVM:

Physical volume
A physical volume (PV) is a partition or whole disk designated for LVM use. For more information, see Managing LVM physical volumes.
Volume group
A volume group (VG) is a collection of physical volumes (PVs), which creates a pool of disk space out of which logical volumes can be allocated. For more information, see Managing LVM volume groups.
Logical volume
A logical volume represents a mountable storage device. For more information, see Managing LVM logical volumes.

The following diagram illustrates the components of LVM:

Figure 1.1. LVM logical volume components

LVM Logical Volume Components

1.2. Advantages of LVM

Logical volumes provide the following advantages over using physical storage directly:

Flexible capacity
When using logical volumes, you can aggregate devices and partitions into a single logical volume. With this functionality, file systems can extend across multiple devices as though they were a single, large one.
Resizeable storage volumes
You can extend logical volumes or reduce logical volumes in size with simple software commands, without reformatting and repartitioning the underlying 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 with user-defined and custom names.
Striped Volumes
You can create a logical volume that stripes data across two or more devices. This can dramatically increase throughput.
RAID volumes
Logical volumes provide a convenient way to configure RAID for your data. This provides protection against device failure and improves performance.
Volume snapshots
You can take snapshots, which is a point-in-time copy of logical volumes for consistent backups or to test the effect of changes without affecting the real data.
Thin volumes
Logical volumes can be thinly provisioned. This allows you to create logical volumes that are larger than the available physical space.
Cache volumes
A cache logical volume uses a fast block device, such as an SSD drive to improve the performance of a larger and slower block device.