IBM SG24-5131-00 manual Alternate Method TaskGuide, Forcing a Varyon

Forcing a Varyon

A volume group with quorum disabled and one or more physical volumes unavailable can be “forced” to vary on by using the -fflag with the varyonvg command. Forcing a varyon with missing disk resources can cause unpredictable results, including a reducevg of the physical volume from the volume group. Forcing a varyon should be an overt (manual) action and should only be performed with a complete understanding of the risks involved.

The HACMP for AIX software assumes that a volume group is not degraded and all physical volumes are available when the varyonvg command is issued at startup or when a volume group resource is taken over during a fallover.

The cluster event scripts provided with the HACMP for AIX software do not “force” varyon with the -fflag, which could cause unpredictable results. For this reason, modifying the cluster event scripts to use the -fflag is strongly discouraged.

Quorum in Non-Concurrent Access Configurations

While specific scenarios can be constructed where quorum protection does provide some level of protection against data corruption and loss of availability, quorum provides very little actual protection in non-concurrent access configurations. In fact, enabling quorum may mask failures by allowing a volume group to varyon with missing resources. Also, designing logical volume configuration for no single point of failure with quorum enabled may require the purchase of additional hardware. Although these facts are true, you must keep in mind that disabling quorum can result in subsequent loss of disks—after varying on the volume group—that go undetected.

Quorum in Concurrent Access Configurations

Quorum must be enabled for an HACMP for AIX concurrent access configuration. Disabling quorum could result in data corruption. Any concurrent access configuration where multiple failures could result in no common shared disk between cluster nodes has the potential for data corruption or inconsistency.

3.4.6 Alternate Method - TaskGuide

The TaskGuide is a graphical interface that simplifies the task of creating a shared volume group within an HACMP cluster configuration. The TaskGuide presents a series of panels that guide the user through the steps of specifying initial and sharing nodes, disks, concurrent or non-concurrent access, volume group name and physical partition size, and cluster settings. The TaskGuide can reduce errors, as it does not allow a user to proceed with steps that

90 IBM Certification Study Guide AIX HACMP