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Set the HA group policy type

 

Overview

The HA group policy type determines which members of a high availability group are automatically made active when the servers containing these members start. We can not directly change the policy type of an existing HA group policy.


Set the policy type

  1. Determine which components are using the HA groups governed by the original policy

  2. Verify these components support the new policy type.

  3. Create a new policy with a different policy type

    You can select one of the following policy types when creating a new policy:

    All active policy All of the members of the HA group are made active.
    M of N policy When selected for an HA group with N members, M of them are made active. The number that M represents is configurable in the policy settings. Use the Preferred servers setting to designate the preference order in which members of the HA group are made active.
    No operation policy None of the HA group members are made active. Use the admin console to manually activate specific group members.
    One of N policy When selected for an HA group with N members, only one member of the group is made active. Use the Preferred servers setting to designate the preference order in which members of the HA group are made active.
    Static policy Only the members specified in the Static group servers setting are made active.

    Messaging engines and the service integration bus only work with the following policy types...

    • Static
    • One of N
    • No operation policy

    The service integration bus component might require a One of N policy, as it only wants one group member active at a given time. An All Active policy might not function properly.

  4. Give the new policy a match criteria so the HA manager selects it to associate with the HA group.

 

Preferred servers setting

With the One of N and M of N policy types, we can set up a list of preferred servers as part of the policy settings, indicating which HA group member is to be made active. If no preferred server list is specified, any of the available HA group members can be selected as the member to activate. The most preferred server is the first one on the list.

 

Failback setting

Specify what happens to the most preferred server after a restart following a failure. When enabled, the currently active member is deactivated, and the most preffered server is activated. When disabled, the currently active member remains the active member.

 

Preferred servers only setting

Instruct the policy to activate members on preferred servers only. If no preferred servers are specified, or no preferred servers are available, no members are activated.

 

Static group servers setting

List of static group servers. The static group server list defines which group members are activated.

 

Is alive timer setting

Controls how frequently the HA manager checks the health of group members. There are two types of failure detection...

Can be specified at the policy level, where it applies to all the members that are governed by the policy, or at the process level, where it applies to all members running in a particular process. We can also disable this type of failure detection at either of these levels.

 

Quorum setting

Used to protect resources that, in the event of a failure, are shared across members of an HA group. When enabled, the policy does not activate any group members until quorum is achieved. A HA group does not achieve quorum until a majority of the members are running.

For example, if there are n members in a group, (n/2) + 1 servers must be online to achieve quorum.

Quorum is designed to work with clusters, specialized component code, and a hardware control facility. Currently, none of the HA groups supporting product components use the quorum mechanism. Therefore, do not enable the Quorum setting.

 

Related

High availability group policy selection process
High availability group policies