Oracle Tips by Burleson

Oracle10g Grid Computing with RAC
Chapter 5 - Preparing Shared Storage

Cluster File System (CFS)

Veritas CFS has evolved from the Veritas File System (VxFS). CFS allows the same file system to be simultaneously mounted on multiple nodes in the cluster. Once again, the CFS is designed with master/slave architecture. Though any node can initiate an operation to create, delete, or resize data, the master node carries out the actual operation. CFS caches the metadata in memory, typically in the memory buffer cache or the vnode cache. A distributed locking mechanism, called GLM, is used for metadata and cache coherency among the multiple nodes.

However, with implementation of the ODM interface, Oracle RAC accesses data files stored on CFS, bypassing the file system buffer and file system locking processes. Oracle manages its own consistency mechanism. The ODM facility is automatically invoked with RAC.

Cluster Volume Management

The cluster volume manager is a software module that virtualizes the physical storage and presents the usable entities for the applications, such as the database at the operating system level. It is a storage administrator layer at the host level.