A cluster might be configured to run a combination of mission-critical services and noncritical services. For example, a database that supports a critical customer service might run in the same cluster as noncritical research tasks.
To ensure that the noncritical services do not affect the performance of the critical service, specify that the critical service has precedence. By specifying that the critical service has precedence, you prevent noncritical services from running on the same node as the critical service.
When all nodes are operational, the critical service runs on a different node from the noncritical services. However, a failure of the critical service might cause the service to fail over to a node where the noncritical services are running. In this situation, the noncritical services are taken offline immediately to ensure that the computing resources of the node are fully dedicated to the mission-critical service.
To specify that a critical service has precedence, declare on the resource group of each noncritical service a strong negative affinity for the resource group that contains the critical service.
# clresourcegroup set|create -p RG_affinities=--critical-rg noncritical-rg
Specifies the resource group that contains a noncritical service. This resource group is the resource group on which you are declaring a strong negative affinity for another resource group.
Specifies the resource group that contains the critical service. This resource group is the resource group for which you are declaring a strong negative affinity.
A resource group moves away from a resource group for which it has a strong negative affinity.
The source of a strong negative affinity might be offline on all nodes when you take offline the target of the strong negative affinity. In this situation, the source of the strong negative affinity is automatically brought online. In general, the resource group is brought online on the most preferred node, based on the order of the nodes in the node list and the declared affinities.
For example, a resource group rg1 declares a strong negative affinity for resource group rg2. Resource group rg1 is initially offline on all nodes, while resource group rg2 is online on a node. If an administrator takes offline rg2, rg1 is automatically brought online.
You can use the clresourcegroup suspend command to prevent the source of a strong negative affinity from being brought online automatically due to strong affinities or cluster reconfiguration.Example 62 Specifying That a Critical Service Has Precedence
This example shows the commands for modifying the noncritical resource groups ncrg1 and ncrg2 to ensure that the critical resource group mcdbrg has precedence over these resource groups. This example assumes that resource groups mcdbrg, ncrg1, and ncrg2 exist.
# clresourcegroup set -p RG_affinities=--mcdbrg ncrg1 ncrg2