Tuning the Storage Subsystem - Expert Oracle RAC Performance Diagnostics and Tuning - page 353

Storage Contention
The path that the host server uses to access the data, the host volume manager, HBA, SAN fabric, and the storage
subsystem controller used in accessing the logical drives should all be configured for optimal performance.
In an Oracle RAC environment the number of nodes and servers accessing the storage subsystem should be taken into
consideration when configuring these access paths. Figure 12-2 illustrates the storage stack and the related software
access paths in a typical storage configuration.

Server SAN

SAN switch

HBA

HBA

HBA

HBA

Operating System

Figure 12-2. Storage access paths

In Figure 12-2 the server has a file system and a volume manger that interface to the storage SAN through the
Fiber Channel and HBA drivers using the HBA cards, SAN switch, and the disk controllers. On the SAN end of the
configuration, the switch will interface with the disk controllers through the various ports. These ports are assigned
to those of the HBA device. The ratio of number of ports mapped to the HBA device depends on the criticality of the
application, the throughput, and the performance requirements. Figure 12-3 illustrates a configuration in which an
HBA is mapped to 16 ports. This is normally not the case in a production environment, where the ratio between the
HBA device to the number of ports is about half. For example, in an Oracle Business Intelligence Enterprise
Edition (OBIEE) production environment configured on an 8-node RAC cluster, each with a dual-port HBA, the HBAs
were mapped to 8 ports on the disk controller.