Users can not access directly, the disk space available on Physical Volumes with in Volume Group. In order to access the space available, the users and applications need to access File Systems which are created on Logical Volumes. Therefore to manage Physical Volume space you need to manage Logical Volumes. For more information you can see the previous article: Aix Logical Volume Manager A Brief Introduction.
Logical Volume Defined
Logical Volumes can be defined as the logical entities which are created from Logical Partitions. While creating Logical Volumes, the number of Logical Partitions are specified.
Mapping To Physical Partition
One Logical Partition maps exactly to one Physical Partitions. But if it’s the case of mirroring then one Logical Partition can map to two or three Physical Partitions as well.
Size of Logical Volume
The size of Logical Volume is determined by the following formula:
Size of LV = Size of LP * No. of LVs * No. of copies of LPs
Components of Logical Volume
Each of the Logical Volume has a Logical Volume Identifier(LVID). It is used to recognize the Logical Volume while using LVM libraries and certain low level commands. LVID format is: VGID.num. The num is the number used to represent the Logical Volume.
Contents of Logical Volume
Each of the Logical Volume contains Logical Volume Control Block. Its better known as LVCB. LVCB takes the first 512 Bytes of Logical Volume. All of the information about Logical Volume is contained there-in. The information is:
- Time of creation.
- Information about mirroring.
- Mount Point(If it has File System created on it.).
I’ll discuss the operations possible on Logical Volumes in some other post.