Conversion of a volume group to nonquorum status

You can change a volume group to nonquorum status to have data continuously available even when there is no quorum.

This procedure is often used for systems with the following configurations:

  • 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

When a volume group under these circumstances can operate in nonquorum status, then even if a disk failure occurs, the volume group remains active as long as at least one disk in the volume group is active.

To make recovery of nonquorum groups possible, ensure the following:
  • If your system uses JFS or JFS2 file systems, mirror the JFS log logical volume.
  • Place mirrored copies on separate disks. If you are unsure of the configuration, type 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

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

Both user-defined and rootvg volume groups can operate in nonquorum status, but their configuration and recovery methods are different.

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.

Attention: When a disk associated with the rootvg volume group is missing, avoid powering on the system 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. LVM must force the activation because the operating system cannot be started unless rootvg is activated. In other words, LVM makes a final attempt to activate (vary on) a nonquorum rootvg even if only a single disk is accessible.