Lazy Update Processing in an HACMP Cluster

For LVM components under the control of HACMP, you do not have to explicitly do anything
to bring the other cluster nodes up to date. Instead, HACMP can perform an importvg -L when
it activates the volume group during a fallover. (In a cluster, HACMP controls when volume
groups are activated.) HACMP implements a function, called lazy update, by keeping a copy
of the time stamp from the volume group’s VGDA. AIX updates this time stamp whenever the
LVM component is modified. When another cluster node attempts to vary on the volume group,
HACMP compares its copy of the time stamp with the time stamp in the VGDA on the disk. If
the values are different, the HACMP software exports and re-imports the volume group before
activating it. If the time stamps are the same, HACMP activates the volume group without
exporting and re-importing.
The following figure illustrates how a lazy update can be achieved in a cluster using the
C-SPOC utility. All nodes in the cluster are updated accordingly, if they are specified from the
node originating the command.



懒得翻译了，大致意思就是，HA在切换的时候会判断一下VGDA的时间戳，如果发现时间戳有更新，说明VG信息需要更新，那会自己export/import一下，所有一般也不用太担心vg信息不一致。