Storage Foundation for Oracle RAC Overview

Storage Foundation for Oracle RAC provides a complete I/O and communications stack to support Oracle RAC. This software also monitors and manages the startup and shutdown of instances. The following section describes the overall data and communications flow of the Storage Foundation for Oracle RAC stack.

Data Stack Overview

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The diagram above details the overall data flow from an instance running on a server to the shared storage. The various Oracle processes making up an instance (such as DB Writer, Log Writer, Checkpoint, and Archiver) read and write data to storage via the I/O stack shown in the diagram. Oracle communicates via the Oracle Disk Manager (ODM) interface to the VERITAS Cluster File System (CFS), which in turn accesses the storage via the VERITAS Cluster Volume Manager (CVM). Each of these components in the data stack is described in this chapter.

Communications Stack Overview

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The diagram above shows the data and communications stacks. Each of the components in the data stack requires communications with its peer on other systems to function properly. RAC instances must communicate to coordinate protection of data blocks in the database. ODM processes must communicate to coordinate data file protection and access across the cluster. CFS coordinates metadata updates for file systems, and CVM coordinates the status of logical volumes and distribution of volume metadata across the cluster. VERITAS Cluster Server (VCS) controls starting and stopping of components in the Storage Foundation for Oracle RAC stack and provides monitoring and notification on failure. VCS must communicate the status of its resources on each cluster node. For the entire system to work, each layer must communicate properly.

The diagram also shows Low Latency Transport (LLT) and Group Membership Services/Atomic Broadcast (GAB), which make up the communications package central to the operation of Storage Foundation for Oracle RAC. During an operational steady state, the only significant traffic through LLT and GAB results from Lock Management and Cache Fusion, while the traffic for the other data is relatively sparse.