The logical volume manager allows you to create and manage the storage of your servers in a very useful manner; adding, removing, and resizing partitions on demand.
There several pieces of terminology that you'll need to understand to make the best use of LVM. The most important things you must know are:
- physical volumes
- These are your physical disks, or disk partitions, such as /dev/hda or /dev/hdb1. These are what you'd be used to using when mounting/unmounting things. Using LVM we can combine multiple physical volumes into volume groups.
- volume groups
- A volume group is comprised of real physical volumes, and is storage used to create logical volumes which you can create/resize/remove and use. You can consider a volume group as a "virtual partition" which is comprised of an arbitary number of physical volumes.
- logical volumes
- These are the volumes that you'll ultimately end up mounting upon your system. They can be added, removed, and resized on the fly. Since these are contained in the volume groups they can be bigger than any single physical volume you might have.
(Example: 4x5Gb drives can be combined into one 20Gb volume group, and you can then create two 10Gb logical volumes.)
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