A volume group is a logical collection of storage space that can span multiple physical devices, used in UNIX and LINUX logical volume management. Physical volumes can be hard drives, disk partitions, or external storage devices, while logical volumes are concatenated storage spaces. The volume group maps logical extents to physical extents, creating a pool of LEs that can be merged into logical volumes. Logical volumes can be scaled up or down by adding or returning LEs to the pool, and a volume group can change size with the addition or removal of a storage unit.
A volume group (VG) is a logical collection, or purposeful grouping, of computer storage space that can span multiple physical devices. Combine physical and logical volumes into a single administrative element within UNIX® and LINUX® logical volume management (LVM). A physical volume can be an internal or external storage device. Logical volumes are concatenations, or linked lists, of storage that could join parts of multiple physical volumes. Under LINUX®, the volume group is the highest level of abstraction, or visualization, in its logical volume management utility.
In early implementations, physical disks were made available to operating systems via static partitions. These partitions can be a sequential portion or all of a single physical device. Each partition would appear to be a separate drive for the operating system. If a partition needed more space, the information on it would have to be transferred to a larger partition on the same or another physical drive.
Many systems, especially those based on UNIX®, now divide physical disk space into standard-sized storage units. Logical volumes composed of units of multiple drives can be allocated to partitions, and storage drives can be added or removed as requirements change. This is the foundation of logical volume management.
Physical volumes can be hard drives, disk partitions, or an external storage device. They are considered a concatenated series of storage spaces called physical extents (PE). These are the basic storage allocation units and, depending on the system, can be uniform or variable in size. Logical volumes similarly consist of logical extents (LEs), which are the same size as physical extents. The volume group’s role is to map logical extents to physical extents, creating a pool of LEs that can be merged into logical volumes or virtual partitions.
Logical volumes can be scaled up or down as needed by simply adding LEs or returning them to the pool. LEs do not have to be sequential or share the same device. A volume group can change size with the addition or removal of a storage unit, although this may require moving or reallocating LEs. However, physical and logical volumes are unique to their volume group and cannot span or be shared by groups. As an administrative unit, a volume group itself can be moved to another host machine, subject to access permissions, or completely hidden.
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