When to create separate volume groups

There are several reasons why you might want to organize physical volumes into volume groups separate from rootvg.

  • For safer and easier maintenance.
    • Operating system updates, reinstallations, and crash recoveries are safer because you can separate user file systems from the operating system so that user files are not jeopardized during these operations.
    • Maintenance is easier because you can update or reinstall the operating system without having to restore user data. For example, before updating, you can remove a user-defined volume group from the system by unmounting its file systems. Deactivate it using the varyoffvg command, then export the group using the exportvg command. After updating the system software, you can reintroduce the user-defined volume group using the importvg command, then remount its file systems.
  • For different physical-partition sizes. All physical volumes within the same volume group must have the same physical partition size. To have physical volumes with different physical partition sizes, place each size in a separate volume group.
  • When different quorum characteristics are required. If you have a file system for which you want to create a nonquorum volume group, maintain a separate volume group for that data; all of the other file systems should remain in volume groups operating under a quorum.
  • For security. For example, you might want to remove a volume group at night.
  • To switch physical volumes between systems. If you create a separate volume group for each system on an adapter that is accessible from more than one system, you can switch the physical volumes between the systems that are accessible on that adapter without interrupting the normal operation of either (see the varyoffvg, exportvg, importvg, and varyonvg commands).