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About CFS

Review CFS File System benefits, CFS configuration differences from VxFS and CFS recovery operations. For introductory information on CFS, see Cluster File System.

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 these benefits:

• Increased manageability, including easy creation and expansion of files. Without a file system, 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.

CFS configuration differences

The first node to mount a CFS file system as shared becomes the primary node for that file system. All other nodes are "secondaries" for that file system.

Use the fsclustadm command from any node to view which node is primary and set the CFS primary node for a specific file system.

Mount the cluster file system individually from each node. The -o cluster option of the mount command mounts the file system in shared mode, which means you can mount the file system simultaneously on mount points on multiple nodes.

When using the fsadm utility for online administration functions on VxFS file systems, including file system resizing, defragmentation, directory reorganization, and querying or changing the largefiles flag, run fsadm from the primary node. This command fails from secondaries.

CFS recovery

The vxfsckd daemon is responsible for ensuring file system consistency when a node crashes that was a primary node for a shared file system. If the local node is a secondary node for a given file system and a reconfiguration occurs in which this node becomes the primary node, the kernel requests vxfsckd on the new primary node to initiate a replay of the intent log of the underlying volume. The vxfsckd daemon forks a special call to fsck that ignores the volume reservation protection normally respected by fsck and other VxFS utilities. vxfsckd can check several volumes at once if the node takes on the primary role for multiple file systems.

After a secondary node crash, no action is required to recover file system integrity. As with any crash on a file system, internal consistency of application data for applications running at the time of the crash is the responsibility of the applications.

Coordinating CVM and CFS configurations

After installing SF Oracle RAC, a VCS cluster attribute (HacliUserLevel) is set to give root the ability to run commands on remote systems by way of the cluster interconnect. CFS takes advantage of this mechanism to enable you to perform file system operations requiring the primary node be initiated on secondary nodes and carried out on the primary node transparently.

If you reset this attribute, be aware of which node is the primary for certain file system operations and perform those tasks from that node. Unlike a non-RAC environment, you cannot run a sequence of VxVM and VxFS commands, such as resizing a volume and a file system, on the same node unless it is both the CVM master and CFS primary node.