Cloning the rootvg to an alternate disk

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Cloning the rootvg to an alternate disk has many advantages. One advantage is having an online backup available, in case of a disk crash. Keeping an online backup requires an extra disk or disks to be available on the system.

Another benefit of rootvg cloning occurs when applying new maintenance or technology level updates. A copy of the rootvg is made to an alternate disk, then updates are applied to that copy. The system runs uninterrupted during this time. When it is rebooted, the system boots from the newly updated rootvg for testing. If updates cause problems, the old_rootvg can be retrieved by resetting the bootlist and then rebooting.

If your current rootvg uses the JFS file system, then the alternate disk cannot have 4K sector sizes.

By default, calling the alt_disk_install command does the following:
  1. Creates an /image.data file based on the current rootvg's configuration. A customized image.data file can be used.
  2. Creates an alternate rootvg (altinst_rootvg).
  3. Creates logical volumes and file systems with the alt_inst prefix.
  4. Generates a backup file list from the rootvg, and if an exclude.list file is given, those files are excluded from the list.
  5. Copies the final list to the altinst_rootvg's file systems.
  6. If specified, the installp command installs updates, fixes, or new filesets into the alternate file system.
  7. The bosboot command creates a boot logical volume on the alternate boot disk.
  8. If a customization script is specified, it runs at this point.
  9. The file systems are then unmounted, and the logical volumes and file systems are renamed.
  10. The logical volume definitions are exported from the system to avoid confusion with identical ODM names, but the altinst_rootvg definition is left as an ODM placeholder.
  11. By default, the bootlist is set to the new cloned rootvg for the next reboot.