5.6.3. Logical Volume Management

One other advanced storage technology is that of logical volume management (LVM). LVM makes it possible to treat physical mass storage devices as low-level building blocks on which different storage configurations are built. The exact capabilities vary according to the specific implementation, but can include physical storage grouping, logical volume resizing, and data migration. Physical Storage Grouping

Although the name given to this capability may differ, physical storage grouping is the foundation for all LVM implementations. As the name implies, the physical mass storage devices can be grouped together in such a way as to create one or more logical mass storage devices. The logical mass storage devices (or logical volumes) can be larger in capacity than the capacity of any one of the underlying physical mass storage devices.
For example, given two 100GB drives, a 200GB logical volume can be created. However, a 150GB and a 50GB logical volume could also be created. Any combination of logical volumes equal to or less than the total capacity (200GB in this example) is possible. The choices are limited only by your organization's needs.
This makes it possible for a system administrator to treat all storage as being part of a single pool, available for use in any amount. In addition, drives can be added to the pool at a later time, making it a straightforward process to stay ahead of your users' demand for storage.