IBM AIX HACMP SG24-5131-00, Hardware User Manual

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IBM Certification Study Guide AIX HACMP
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
-f
flag 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
-f
flag, which could cause unpredictable results. For
this reason, modifying the cluster event scripts to use the
-f
flag 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