Chapter 4. Logical Volume Manager (LVM)

Beginning with Red Hat Linux 8.0, Logical Volume Manager (LVM) is available for hard drive allocation.

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 you want to have the root / partition on a logical volume, you will need to 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, if you want the logical volume group to span over more than one drive, you must 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 kernel for Red Hat Linux 9 is compiled with LVM support.

To learn how to configure LVM during the Red Hat Linux installation process, refer to Chapter 11 LVM Configuration.