A hierarchy of structures is used to manage fixed-disk storage. Each individual fixed-disk drive, called a physical volume (PV) has a name, such as /dev/hdisk0. Every physical volume in use belongs to a volume group (VG). All of the physical volumes in a volume group are divided into physical partitions (PPs) of the same size. The size is determined by the capacity of the physical disk. In general a single disk can not be configured with more than 1016 PPs. The PP size must be adjusted to maintain this limit. This action can be altered by creating a Big Volume Group, but depending on the size of the PPs the number of physical volumes in the volume group will be reduced. For space-allocation purposes, each physical volume is divided into five regions (outer_edge, inner_edge, outer_middle, inner_middle and center). The number of physical partitions in each region varies, depending on the total capacity of the disk drive.

NORMAL VOLUME GROUP (no -B option)

Within each volume group, one or more logical volumes (LVs) are defined. Logical volumes are groups of information located on physical volumes. Data on logical volumes appears to be contiguous to the user but can be discontiguous on the physical volume. This allows file systems, paging space, and other logical volumes to be resized or relocated, span multiple physical volumes, and have their contents replicated for greater flexibility and availability in the storage of data.

Each logical volume consists of one or more logical partitions (LPs). Each logical partition corresponds to at least one physical partition. If mirroring is specified for the logical volume, additional physical partitions are allocated to store the additional copies of each logical partition. Although the logical partitions are numbered consecutively, the underlying physical partitions are not necessarily consecutive or contiguous.

Logical volumes can serve a number of system purposes, such as paging, but each logical volume that holds ordinary system or user data or programs contains a single journaled file system (JFS). Each JFS consists of a pool of page-size (4KB) blocks. When data is to be written to a file, one or more additional blocks are allocated to that file. These blocks may or may not be contiguous with one another or with other blocks previously allocated to the file. In AIX 4.1, a given file system can be defined as having a fragment size of less than 4KB (512 bytes, 1KB, 2KB).

 After installation, the system has one volume group (the rootvg volume group) consisting of a base set of logical volumes required to start the system and any others you specify to the installation script. Any other physical volumes you have connected to the system can be added to a volume group (using the extendvg command). You can add the physical volume either to the rootvg volume group or to another volume group (defined by using the mkvg command). Logical volumes can be tailored using the commands or the menu-driven System Management Interface Tool (SMIT) interface.

This data was taken from an AIX document, to continue reading please visit Logical Volume Storage Overview

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