About the Round Robin policy
The Round Robin policy chooses a resource that satisfies all the service-specific quota requirements from a pool in a round-robin manner. In Unify, each resource is assigned an incremental identifier (ID), when it is added through the Unify control panel.
This policy chooses a resource randomly for the first time, and then it selects the next resource in the increasing order of the resource's identifier (ID). Once the resource with the highest ID has been used for provisioning, the next resource that will be selected will be the one with the lowest ID, and so on.
To use incremental resource IDs, Unify stores the value of the last-used resource's ID for each service on the provisioning engine (PE) server.
Therefore, if the Provisioning Engine COM+ service on a PE server is restarted, the value of the last resource ID is lost, and the Round Robin policy again chooses a resource randomly.
If you have multiple PE servers, each PE server may have a different value for the last resource ID for the same service and pool since the Round Robin policy chooses a resource randomly for the first time. Therefore, depending on to which PE server the provisioning request is sent, the resources in a pool will be utilized differently.
If a resource does not satisfy all the service-specific quota requirements, then the Round Robin policy keeps on checking the next resource in the pool with a higher ID value until it finds a resource that satisfies all the requirements. Due to this, if most of the resources in a pool are heavily utilized for provisioning, this policy will loop through all the resources in the pool and always choose those, which have very high or unlimited quotas.
Example: The service provider has access to four resources with resource IDs as 1, 2, 3, and 4. If the service provider now tries to provision a service to an organization, and all the four resources satisfy all the service-specific quota requirements, the Round Robin policy will choose any resource randomly for the first service provision. Let us assume that it selects the resource with ID 2. For the consecutive service provisions, the policy selects the resources with incremental IDs, that is, 3, 4, 1, 2, and so on.