Mirroring the ROOT VG

The following scenario explains how to mirror the root volume group (rootvg).

Note:

1. Mirroring the root volume group requires advanced system administration experience. If not done correctly, you can cause your system to be unbootable.
2. Mirrored dump devices are supported in AIX® 4.3.3 or later.

In the following scenario, the rootvg is contained on hdisk01, and the mirror is being made to a disk called hdisk11:

1. Check that hdisk11 is supported by AIX as a boot device:

   bootinfo -B hdisk11

   If this command returns a value of 1, the selected disk is bootable by AIX. Any other value indicates that hdisk11 is not a candidate for rootvg mirroring.
2. Extend rootvg to include hdisk11, using the following command:

   extendvg rootvg hdisk11

   If you receive the following error messages:

   0516-050 Not enough descriptor space left in this volume group, Either try
   adding a smaller PV or use another volume group.

   or a message similar to:

   0516-1162 extendvg: Warning, The Physical Partition size of 16 requires the
   creation of 1084 partitions for hdisk11. The limitation for volume group
   rootvg is 1016 physical partitions per physical volume. Use chvg command with
   the -t option to attempt to change the maximum physical partitions per Physical
   Volume for this volume group.

   You have the following options:

   • Mirror the rootvg to an empty disk that already belongs to the rootvg.
   • Use a smaller disk.
   • Change the maximum number of partitions supported by the rootvg, using the following procedure:
     1. Check the message for the number of physical partitions needed for the destination disk and the maximum number currently supported by rootvg.
     2. Use the chvg -t command to multiply the maximum number of partitions currently allowed in rootvg (in the above example, 1016) to a number that is larger than the physical partitions needed for the destination disk (in the above example, 1084). For example:

        chvg -t 2 rootvg

     3. Reissue the extendvg command at the beginning of step 2.
3. Mirror the rootvg, using the exact mapping option, as shown in the following command:

   mirrorvg -m rootvg hdisk11

   This command will turn off quorum when the volume group is rootvg. If you do not use the exact mapping option, you must verify that the new copy of the boot logical volume, hd5, is made of contiguous partitions.
4. Initialize all boot records and devices, using the following command:

   bosboot -a

5. Initialize the boot list with the following command:

   bootlist -m normal hdisk01 hdisk11

   Note:

   1. Even though the bootlist command identifies hdisk11 as an alternate boot disk, it cannot guarantee the system will use hdisk11 as the boot device if hdisk01 fails. In such case, you might have to boot from the product media, select maintenance, and reissue the bootlist command without naming the failed disk.
   2. If your hardware model does not support the bootlist command, you can still mirror the rootvg, but you must actively select the alternate boot disk when the original disk is unavailable.