Changing a Volume Group to Nonquorum Status

AIX Version 4.3 System Management Guide: Operating System and Devices

Changing a Volume Group to Nonquorum Status

The purpose of a nonquorum volume group is to have data continuously available even when there is no quorum. A quorum is a state in which 51% or more of the physical volumes in a group are accessible. You might want to change a volume group to nonquorum status in systems configured as follows:

A two-disk volume group in which the logical volumes are mirrored.
A three-disk volume group in which the logical volumes are mirrored either once or twice.

In either configuration, if a disk failure occurs, the volume group remains active as long as there is one logical volume copy intact on a disk.

Both user-defined and rootvg volume groups can operate in nonquorum status, but the methods used to configure them as nonquorum and for recovery after hardware failures are different for user-defined and rootvg volume groups.

Attention: If a logical volume has its only copies residing on a disk that becomes unavailable, the information will not be available to the user regardless of the quorum or nonquorum status of the volume group.

Prerequisites

To make recovery of nonquorum groups possible, make sure to:
- Mirror the JFS log logical volume if JFS file systems are in use on the system.
- Place the copies on separate disks. If you are unsure of the configuration, use the following command to check the physical location (PV1, PV2, and PV3) of each logical partition. (To place the copies on separate disks, the PV1, PV2, and PV3 columns must contain different hdisk numbers.):
```
lslv -m LVName
```
Be sure you read and understand the following before attempting to mirror nonquorum volume groups:
- "Logical Volume Storage Overview".
- "Developing a Volume Group Strategy".

Changing User-Defined Volume Groups to Nonquorum Status

To activate a nonquorum user-defined volume group, all of the volume group's physical volumes must be accessible or the activation fails. Because nonquorum volume groups stay online until the last disk becomes inaccessible, it is necessary to have each disk accessible at activation time.

Run the following command to see whether the user-defined volume group is varied on.
```
lsvg -o
```
If the user-defined volume group does not appear in the list, follow step 3. Otherwise, follow step 2.
To make a standard user-defined volume group a nonquorum volume group, use the following command;
```
chvg -Qn VGName
```
If the volume group is not active (varied on), use the following command to activate it and make effective the change to nonquorum status:
```
varyonvg VGName
```
If the volume group is already activated (varied on), use the following commands to make the change to nonquorum status effective:
```
varyoffvg VGname
```
then:
```
chvg -Qn VGName
```
then:
```
varyonvg VGName
```

Changing the rootvg Volume Group to Nonquorum Status

Note: Do not power on the system when a disk associated with the rootvg volume group is missing unless the missing disk cannot possibly be repaired. The Logical Volume Manager (LVM) always uses the -f flag to forcibly activate (vary on) a nonquorum rootvg; this operation involves risk. The reason for the forced activation is that the system cannot be brought up unless rootvg is activated. In other words, LVM makes a last ditch attempt to activate (vary on) a nonquorum rootvg even if only a single disk is accessible.

To make rootvg a nonquorum volume group, use the following command:
```
chvg -Qn rootvg
```
Shut down and reboot the system to make effective the change to nonquorum status:
```
shutdown -Fr
```