Type of Database licensing for SAP:
The type of licensing impacts the cluster design for SAP virtualization. SAP is supported on most common database platforms such as SQL, Oracle, DB2 and SYBASE. When customers procure SAP, they can choose to buy the database licensing through SAP or purchase it directly from the database vendor. This decision impacts the cluster design for virtualized SAP environments.
Let us look at these two scenarios and their impact on the design.
Scenario 1: Database License procured from the DB vendor for SAP:
Database vendors have differing but usually very restrictive policies regarding virtual machines running databases. The cost of licensing databases in the extreme case could force a customer to license for the entire cluster, even though the database could be using only a small subset of the resources. Due to the uncertainty and the risk involved with DB licensing in this situation, it might be prudent to separate the entire database workload into its own cluster. By separating the entire database workload, the physical hardware used for databases can be isolated and licensed fully. Since only database workloads exist in this cluster one can achieve consolidation and efficiency for databases. The main disadvantage is the added overhead of having a separate cluster for databases. Since SAP landscapes have many modules with each module having its own individual database, creating a separate DB cluster with a good number of hosts is worthwhile and justified.
Dedicated Database Cluster for SAP
When there are no restrictions with licensing, the typical cluster design methodology in vSphere environments espouses having an N+2 cluster. An N+2 cluster would provide headroom for doing maintenance (One host at a time) and high availability (One host failure). These additional hosts can be costly for the database cluster due to the need to license all hosts. In this situation the applications run in their own cluster, which typically is N+2.
SAP Applications in their own cluster
Dedicated APP Cluster for SAP
Most database vendors allow for a non licensed DB host, if the only purpose of these hosts is to function as a standby in the event of a failure. There are many conditions such as the number of actual days the standby takes over per year and other requirements that need to be met. vSphere clusters have a setting called dedicated failover host, which can be leveraged in database clusters to match the requirements of standby hosts. One can potentially meet these conditions for standby node, by running all workloads in normal circumstances on licensed nodes with the dedicated failover node minimally being used only during actual failure or maintenance.
Scenario 2: Database licensed through SAP along with SAP software:
When databases are licensed through SAP, there is no impact of database placement on licensing. This is akin to “named user” based licensing. There is a lot more flexibility to locate the database servers anywhere in the environment. Customers typically collocate the database servers along with the application servers for proximity and ease of management. The commonly used N+2 clusters can be leveraged in this scenario to allow for HA capacity even during maintenance. All nodes can be fully utilized to run workloads.
SAP Applications and Databases in the same cluster
Conclusion:
Cluster design in SAP environments can be impacted by the type of database licensing. Creating a dedicated database cluster for certain situation, can help meet many of the stringent licensing requirements, while still providing for consolidation and optimized utilization.
