Volume Group:
Multiple Physical Volumes (initialized partitions) are merged into a Volume Group (VG). This is done with the command: vgcreate test_vg /dev/sdc1 /dev/sde1. Both sdc1 and sde1 must be PV’s. The VG named test_vg now has the combined capacity of the two PV’s and more PV’s can be added at any time. This step also registers test_vg in the LVM kernel module. Two of the most important components of the volume group are the volume group descriptor area (VGDA) and volume group status area (VGSA).
The VGDA is an area at the front of each disk, which contains information about the volume group, the logical volumes that reside on the volume group. This VGDA, the metadata is replicated on each disk in the volume group. This VGDA area is also used in quorum voting. The VGDA contains information about what other disks make up the volume group. This information is what allows the user to just specify one of the disks in the volume group when they are using the “importvg” command to import a volume group into an AIX [18] system. The importvg will go to that disk, read the VGDA and find out what other disks (by PVID) make up the volume group and automatically import
those disks into the system (and its) ODM as well. The information about neighboring disks can sometimes be useful in data recovery. For the logical volumes that exist on that disk, the VGDA gives information about that logical volume so anytime some change is done to the status of the logical volume (creation, extension, or deletion), then the VGDA on that disk and the others in the volume group must be updated. The following excerpt has been taken from the actual LVM code in Linux:
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