The SAN connectivity, which includes host bus adapters (HBAs), SAN ports, switches, and array front-end ports, requires careful planning. The SAP HANA KPIs for TDI deployments require a maximum bandwidth of 400 MB/s per SAP HANA node. For example, if 24 nodes in a SAN are connected to a PowerMax array, a total bandwidth of 9,600 MB/s is required. Assuming that a 16 Gbps front-end port provides approximately 3,000 MB/s of bandwidth, at least four dedicated 16 Gbps front-end ports are required to support 10 SAP HANA nodes (4 x 3,000 MB/s = 12,000 MB/s).
While this maximum bandwidth requirement only arises in the unlikely event that all nodes require the maximum bandwidth simultaneously, the ability of storage arrays to sustain this peak workload is one of the SAP HANA certification criteria.
This maximum bandwidth requirement does not affect only the storage front-end configuration. In the example with 24 nodes, the complete path through the SAN network must be configured to support the maximum bandwidth. In a multihop SAN, where multiple switches are connected through Inter-Switch Links (ISLs), the bandwidth of the ISLs must also support the required bandwidth.
When you are planning storage connectivity for performance and availability, we recommend “going wide before going deep.” In other words, connecting storage ports across different engines and directors is preferable to using all the ports on a single director. Even if a component fails, the storage can continue to service host I/O.
Dynamic core allocation, where each director provides services such as front-end connectivity, back-end connectivity, and data management, is available with the PowerMax arrays. Each service has its own set of cores on each director. The cores are pooled to provide CPU resources that can be allocated as necessary. For example, even if host I/O arrives through a single front-end port on the director, the front-end pool with all its CPU cores will be available to service that port. Because I/O arriving to other directors has its own core pools, for best performance and availability connect each host to ports on different directors before using additional ports on the same director.
SAP requires isolation of the SAP HANA workload from non SAP HANA applications. Thus, we recommend using dedicated front-end ports for SAP HANA and not sharing these ports with non SAP HANA applications.
To connect a host or cluster, we recommend the following best practices:
The following figure shows SAN connectivity in a single-engine environment:
Figure 3. SAN connectivity in a single-engine environment
Each HBA port (initiator) creates a path for I/O between the host and the SAN switch, which then continues to the PowerMax storage. Use two HBA ports, preferably on two separate HBAs. Two ports provide more connectivity and also enable the Linux native multipathing (DM-MPIO) to load-balance and fail over across HBA paths.