Veritas Storage Foundation 5.1 SP1 for Oracle RAC Administrator"s Guide (5900-1512, April 2011)

metadata, such as inodes and free lists. The role of GLM is set on a per-file system
basis to enable load balancing.
CFS involves a primary/secondary architecture. One of the nodes in the cluster
is the primary node for a file system. Though any node can initiate an operation
to create, delete, or resize data, the GLM master node carries out the actual
operation. After creating a file, the GLM master node grants locks for data
coherency across nodes. For example, if a node tries to modify a block in a file, it
must obtain an exclusive lock to ensure other nodes that may have the same file
cached have this cached copy invalidated.
SF Oracle RAC configurations minimize the use of GLM locking. Oracle RAC
accesses the file system through the ODM interface and handles its own locking;
only Oracle (and not GLM) buffers data and coordinates write operations to files.
A single point of locking and buffering ensures maximum performance. GLM
locking is only involved when metadata for a file changes, such as during create
and resize operations.
CFS communication
CFS uses port f for GLM lock and metadata communication. SF Oracle RAC
configurations minimize the use of GLM locking except when metadata for a file
changes.
CFS file system benefits
Many features available in VxFS do not come into play in an SF Oracle RAC
environment because ODM handles such features. CFS adds such features as high
availability, consistency and scalability, and centralized management to VxFS.
Using CFS in an SF Oracle RAC environment provides the following benefits:
■ Increased manageability, including easy creation and expansion of files
In the absence of CFS, you must provide Oracle with fixed-size partitions. With
CFS, you can grow file systems dynamically to meet future requirements.
■ Less prone to user error
Raw partitions are not visible and administrators can compromise them by
mistakenly putting file systems over the partitions. Nothing exists in Oracle
to prevent you from making such a mistake.
■ Data center consistency
If you have raw partitions, you are limited to a RAC-specific backup strategy.
CFS enables you to implement your backup strategy across the data center.
33Overview of Veritas Storage Foundation for Oracle RAC
Component products and processes of SF Oracle RAC