Hi Cluster Fans,

A few weeks ago I posted a blog about configuring IP Addresses with multiple subnets and got some feedback about some additional scenarios to consider.  This blog post will discuss the best practice of setting possible owners for the IP Addresses.

Setting Possible Owners

The ‘Possible Owners’ setting is a resource property which allows an admin to designate whether a resource should come online on a specific node.  By default, all nodes in the cluster will be the possible owner of a resource.  However, you may want a workload to never come online on a specific node, so you will want to adjust these settings to prevent the cluster from trying to start the resource on that node.  The resource will be able to move to a non-possible owner, however it will never automatically come online on that node.

An IP Address resource in a multi-subnet cluster is a perfect example of why you may want to configure this property.  In our example from the previous blog post we deployed a File Server that used two subnets, a 172.24.13.0/24 and a 172.24.14.0/24.   We will refer to these as our “.13 Subnet” and “.14 Subnet”, respectively.   We configured two IPv4 Addresses, 172.24.13.1 on my .13 Subnet and 172.24.14.1 on my .14 Subnet.  Since the .13 IP Address will only come online on nodes which are on the .13 Subnet, only those nodes should be possible owners.  Since the .14 IP Address will only come online on nodes which are on the .14 Subnet, only those nodes should be possible owners. 

Although configure Possible Owners is not required for multi-subnet clustering, it is a best practice since it reduces the amount of work which the cluster has to do after a failover since it will never try to bring those IP Addresses online on nodes which will never support it.

To configure Possible Owners, right-click on each IP Address resource and select Properties, then the Advanced Policies tab.  Toggle the Possible Owners to the correct setting then click Apply and exit.  Make sure you do this for both IP Address resources.

In our example, symonp-N1 is on our .14 Subnet, and symonp-N2 is on our .13 Subnet.  This means that we want to make symonp-n1 the Possible Owner for the .14 IP Address and symonp-n2 the Possible Owner for the .13 IP Address. 

Now your IP Address resources will only come online on the appropriate cluster nodes.

This KB article contains a great summary of the semantics of the various cluster ownership policies: http://support.microsoft.com/kb/299631.  

Thanks,

Symon Perriman
Program Manager II
Clustering & High-Availability
Microsoft