Oracle Parallel Processing

Disk Affinity

An OPS instance is said to have affinity for a device if the device is directly accessible from the node on which the instance is running. Figure 13.2 shows two instances on two different nodes: disk A is directly connected to node 1, and disk B is directly connected to node 2. A high-speed interconnect makes this configuration a shared disk architecture in which both disks are accessible from both nodes.

Figure 13-2. Disk affinity

Since disk A is local to node 1, the instance running on that node is said to have affinity for disk A. In this case, instance 1 has affinity for disk A. Similarly; instance 2 has affinity for disk B. I/O operations will be faster and more efficient when an instance is accessing disks for which it has affinity.

Extending the device-to-instance affinity concept to datafiles, an instance has affinity for a file if it has affinity for the disk on which that file is stored. In Figure 13.2, instance 1 has affinity for files stored on disk A, and instance 2 has affinity for files stored on disk B.

When allocating parallel execution tasks to parallel slave processes on multiple nodes, Oracle takes disk affinity into account. However, this affinity is transparent to the application or user invoking the task.

Disk Affinity is Platform-Specific

Not all platforms recognize disk affinity. Please refer to your platform-specific documentation, or contact Oracle ...