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Lesson 10The logical volume approach
Objective Describe the use of a logical volume system to overcome the limitations of a filesystem based on disk partitions.

Logical Volume Approach

The traditional approach to filesystems, based on disk partitions, has some limitations. Some are:
  1. Changing the layout of partitions on a disk after filesystems have been installed is difficult.
  2. Partitions cannot span physical disks.
  3. Techniques such as striping are not available.
The logical volume approach to managing filesystems helps to deal with some of these problems. AIX and HP-UX take advantage of logical volumes; on AIX, there is no other option. In the logical volume system, groups of physical disks are combined together into volume groups. These volume groups can be divided up into logical volumes. These logical volumes may span multiple physical disks, but they act like partitions in the old sense of the word. A logical volume, for example, contains a filesystem. In the logical volume world, you mount and unmount logical volumes, not disk partitions.
To summarize the procedure:
  1. A group of disks is packaged together into a volume group.
  2. The volume group is split into logical volumes of desired size.
  3. A filesystem is installed on each logical volume.
  4. The logical volumes are mounted and unmounted as if they were actual partitions.

What is the logical volume approach to managing filesystems in Unix?

The Logical Volume Manager (LVM) is a method of managing disk storage on Unix-like operating systems. It allows for logical volumes to be created, which can span across multiple physical disks or partitions. These logical volumes can be resized or moved without requiring changes to the underlying physical storage.
The LVM approach to managing filesystems involves the following steps:
  1. Physical storage is divided into one or more physical volumes (PVs). These can be disks, disk partitions, or even whole disks.
  2. One or more PVs are combined into a volume group (VG). A VG is a pool of disk space that can be allocated to logical volumes.
  3. Logical volumes (LVs) are created within a VG. An LV is a virtual partition that can be formatted with a filesystem and mounted like any other partition.
  4. LVs can be resized or moved without affecting the underlying physical storage. This allows for easy management of disk space without having to repartition disks.
  5. Additional PVs can be added to a VG, and LVs can be created or moved between VGs. This provides a great deal of flexibility in managing storage on a system.

Overall, the LVM approach to managing filesystems provides a lot of flexibility and allows for easy management of disk space on Unix-like systems. It is widely used in enterprise environments where disk management is a critical task.