4.1. What is LVM?

LVM is a method of allocating hard drive space into logical volumes that can be easily resized instead of partitions.

With LVM, the hard drive or set of hard drives is allocated to one or more physical volumes. A physical volume can not span over more than one drive.

The physical volumes are combined into logical volume groups, with the exception of the /boot/ partition. The /boot/ partition can not be on a logical volume group because the boot loader can not read it. If the root / partition is on a logical volume, create a separate /boot/ partition which is not a part of a volume group.

Since a physical volume can not span over more than one drive, to span over more than one drive, create one or more physical volumes per drive.

The logical volume group is divided into logical volumes, which are assigned mount points such as /home and / and file system types such as ext3. When "partitions" reach their full capacity, free space from the logical volume group can be added to the logical volume to increase the size of the partition. When a new hard drive is added to the system, it can be added to the logical volume group, and the logical volumes that are the partitions can be expanded.

On the other hand, if a system is partitioned with the ext3 file system, the hard drive is divided into partitions of defined sizes. If a partition becomes full, it is not easy to expand the size of the partition. Even if the partition is moved to another hard drive, the original hard drive space has to be reallocated as a different partition or not used.

LVM support must be compiled into the kernel. The default Red Hat kernel is compiled with LVM support.

To learn how to configure LVM during the installation process, refer to Chapter 13 LVM Configuration.