Alternate Disk Installation

On System where the downtime is critical, AIX offers an additional way to install a system. The Alternate Disk Installation allows installing a system while it is still up and running, thus decreasing the installation or down time.

Alternate Disk Installation is used for:
• Installation of mksysb image on another disk, for example a mksysb from a machine with similar hardware that already has been upgraded.
• Cloning an existing rootvg on another disk. Optionally, the cloning offers the possibility of installing updates and new file sets to the cloned rootvg.

The command used for Alternate Disk Installation is alt_disk_install.

The command creates an altinst_rootvg volume group on the destination disk and prepares the same logical volume groups as in the rootvg, except the names are prepended with alt_ (for example, alt_hd1). Similar are the file systems renamed to /alt_inst/filesystemname, and the original data (mksysb or rootvg) is copied.

After this first phase, a second phase begins where an optional configuration action can be performed.

The third phase unmounts the /alt_inst/ file systems and renames the file systems and logical volumes by removing the alt names. When this is done, the altinst_rootvg is varied off, and the bootlist is altered to boot from the new disk.

After the system is rebooted, the original rootvg is renamed to old_rootvg.

The Alternate Disk Installation requires the file sets bos.alt_disk_install.boot_images and bos.alt_disk_install.rte to be installed.

Below is the example that shows the use of alt_disk_install command, performing a cloning of running rootvg on hdisk0 to an unused hdisk1:

# lspv
hdisk0 0001fd4f703db420 rootvg active
hdisk1 0001fd4f72df8da7 None
# bootinfo –b (device from which system boot last time)
hdisk0

# bootlist -m normal –o (bootlist for normal mode)
hdisk0


# alt_disk_install -C hdisk1
+-----------------------------------------------------------------------------+
ATTENTION: calling new module /usr/sbin/alt_disk_copy. Please see the alt_disk_copy man page and documentation for more details.
Executing command: {/usr/sbin/alt_disk_copy -d "hdisk1"}
+-----------------------------------------------------------------------------+
Calling mkszfile to create new /image.data file.
Checking disk sizes.
Creating cloned rootvg volume group and associated logical volumes.
Creating logical volume alt_hd5
Creating logical volume alt_hd6
Creating logical volume alt_hd8
Creating logical volume alt_hd4
Creating logical volume alt_hd2
Creating logical volume alt_hd9var
Creating logical volume alt_hd3
Creating logical volume alt_hd1
Creating logical volume alt_hd10opt
Creating /alt_inst/ file system.
Creating /alt_inst/home file system.
Creating /alt_inst/opt file system.
Creating /alt_inst/tmp file system.
Creating /alt_inst/usr file system.
Creating /alt_inst/var file system.
Generating a list of files
for backup and restore into the alternate file system...
Backing-up the rootvg files and restoring them to the
alternate file system...
Modifying ODM on cloned disk.
Building boot image on cloned disk.
forced unmount of /alt_inst/var
forced unmount of /alt_inst/usr
forced unmount of /alt_inst/tmp
forced unmount of /alt_inst/opt
forced unmount of /alt_inst/home
forced unmount of /alt_inst
forced unmount of /alt_inst
Changing logical volume names in volume group descriptor area.
Fixing LV control blocks...
Fixing file system superblocks...
Bootlist is set to the boot disk: hdisk1

# lspv (Change in lspv after alt_disk_install command)
hdisk0 0001fd4f703db420 rootvg active
hdisk1 0001fd4f72df8da7 altinst_rootvg

# bootlist -m normal –o (New bootlist after alt_disk_install command)
hdisk1

Next time the system will boot from hdisk1 and the original rootvg will be renamed as old_rootvg.

# lspv
hdisk0 0001fd4f703db420 old_rootvg
hdisk1 0001fd4f72df8da7 rootvg active

Now you can do various testing on hdisk1 (new rootvg). For example, upgraded the Maintenance level or software and check whether the application or system is running fine?


If you want to build another server (Server2) having similar hardware setup with the same rootvg as it is in existing server (Server1). Follow the below steps in Server1:
• exportvg altinst_rootvg
• rmdev –Rdl hdisk1
• Remove hdisk1 of Server1 and replace it with hdisk0 of Server2.
• Boot Server2 from hdisk0
• Change some of the important parameters like IP address, hostname etc.