Controlling Application Move with Preference Values
Controlling application move and server management is done with preference values. Preference values range from 0 through 3200. They express the importance of each individual member of the group.
Note that only MOVE groups and SERVER groups support preference values. With BASIC groups you cannot specify preferences, because all members need to be available. For MOVE and SERVER groups, the preference defines which resource members of the group should preferably run. Remember that a MOVE group is designed for backup solutions. A MOVE group can have many components, but one and only one is supposed to be active. All other components are for backup only. Thus MOVE groups usually contain members of one kind (where one application can replace the others).
SERVER groups are created when only a certain number of their resources need to be available for the application group to be available. The number of desired available resources is controlled by the Availability Target parameter in the customization dialog. You can use the preference value in the customization dialog to control which resources you want to be available and which you want to keep as backups.
The effective preference of each group member is calculated to determine which group members get picked to be activated by the group. The primary inputs into this are the base preference (as specified through the customization dialogs) and the preference adjustment (specified indirectly through the INGGROUP interface). These are added together to produce the resource's adjusted preference (this is the same as the preference value you actually enter the INGGROUP panels).
The following modifiers are then applied to the resource's adjusted preference if it is >1:
| Bonus | Reason |
|---|---|
| 25 | Member is currently selected and has an adjusted preference ≤1000. |
| 175 | Member is currently selected and has an adjusted preference >1000. |
| 220 | Member has an observed status of Starting, Stopping or Degraded and the system is not being stopped. |
| 225 | Member has an observed status of Available and the system is not being stopped. |
| –400 | Member has an adjusted preference >1500 and either the system is being stopped or the system has already been stopped and the member thus has an observed status of SysGone. |
The working value for the preference may then be set to an absolute value if any of the following conditions are satisfied:
- A member with an effective preference of 1 may never be picked. It must always be sent a MakeUnavailable vote.
- A member with an effective preference <600 may only be picked if the group is in recovery mode (that is, it is recovering from a failure).
- A member requiring a resource on an excluded system must be sent a MakeUnavailable vote, even if it has been picked. This can occur with resources that have adjusted preferences >2600.