This section provides guidance for determining the number of IP addresses required for a new cluster implementation. The following guidance does not apply to all clusters and is provided as a reference for the process and considerations during a new cluster implementation.

During the process of implementing a new cluster and building the network topology, consider the following information and recommendations:

• Calculate the number of IP addresses that are needed based on future cluster size, not the initial cluster size.
• Do not share a subnet with other application servers. If more IP addresses are required, and the range is full, readdressing an entire cluster and then moving it into a new VLAN is disruptive. These complications are prevented with proper planning.
• Static IP pools require one IP address for each logical interface that will be in the pool. Each node provides two interfaces for external networking. If Link Aggregation is not configured, this would require 2*N IP addresses for a static pool.
• Use one IP address for each SmartConnect Service IP (SSIP)
• For optimal load-balancing, during a node failure, IP pools with the dynamic allocation method require the number of IP addresses at a minimum of the node count and a maximum of the client count. For example, a 12-node SmartConnect zone and 50 clients, would have a minimum of 12 and a maximum of 50 IP addresses. In many larger configurations, defining an IP address per client is not feasible, and in those cases, the optimal number of IP addresses is workflow-dependent and based on lab testing. In the previous examples, N*(N-1) is used to calculate the number of IP addresses, where N is the number of nodes that will participate in the pool. For larger clusters, this formula might not be feasible due to the sheer number of IP addresses. Determining the number of IP addresses within a dynamic allocation pool varies depending on the workflow, node count, and the estimated number of clients that would be in a failover event.
• If more than a single access zone is configured with IP pools using the dynamic allocation method, examine if all the pools are required. Reducing the number of IP pools, will also reduce the number of IP addresses required.
• If a cluster has multiple access zones or IP pools, a lower number of IP addresses might be required. If so, consider reducing the total number of IP addresses. Generally, as more access zones and IP address pools are configured, fewer IP addresses are required.

In previous OneFS releases, a greater IP address quantity was recommended, considering the typical cluster size and the workload a single node could handle during a failover. As nodes become unavailable, all the traffic hosted on that node is moved to another node with typically the same resources, which could lead to a degraded end-user experience. Because PowerScale nodes are now in the 7th generation, this is no longer a concern. Each node does have limitations, which must be considered when determining the number of IP addresses and failover events creating additional overhead. Also, as OneFS releases have progressed, so has the typical cluster size, making it difficult to maintain the N*(N-1) formula with larger clusters.

From a load-balancing perspective, for dynamic pools, it is ideal for all the interfaces to have the same number of IP addresses whenever possible. In addition to keeping in mind the preceding points, consider the workflow and failover requirements set by IT administrators.