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Cluster File System (CFS)

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

Cluster File System (CFS) offers a very good shared storage facility for building the RAC database. CFS provides a shared file system which is mounted on all the cluster nodes simultaneously. When implementing RAC database with commercial CFS products such as the Veritas CFS or PolyServe Matrix Server, many different kinds of databases files will be able to be stored including the shared Oracle Home and CRS Home.

However the capabilities of the CFS products are not the same. For example, Oracle CFS (OCFS) used in Linux RAC implementations has limitations. It is not a general purpose file system. It cannot be used for shared Oracle Home. Figure 5.5 shows the files locatable on a Cluster File System.

Figure 5.5: Using cluster file system for shared storage structures

A cluster file system (CFS) is a file system that may be accessed by all the members in the cluster at the same time. This implies that all the members of the cluster have the same view. Some of the popular and widely used cluster file system products for Oracle RAC include: HP Tru64 CFS, Veritas CFS, IBM GPFS, Polyserve Matrix Server, and Oracle Cluster File system. The cluster file system offers:

* Simple management.

* The use of Oracle Managed Files with RAC.

* A Single Oracle Software Installation.

* Auto-extend Enabled on Oracle Data Files.

* Uniform accessibility of Archive Logs.

* ODM compliant File systems.

In these author?s opinions, when the cluster file system is available for a given platform, it is preferable to use the CFS rather that the raw partitions. With the availability of the ODM-compliant cluster file systems, using the CFS makes much more sense. ODM-based CFS offer similar or even better performance over raw partitions, and far superior administrative convenience. The cluster file system set of features is rapidly advancing. A detailed explanation of the cluster file system, as well as advances in usage and functionality, will be offered in later sections of the chapter.

ASM ? Automatic Storage Management

ASM is the new star on the block. ASM provides a vertical integration of the file system and volume manager for Oracle database files. ASM has the capability to spreads database files across all available storage for optimal performance and resource utilization. It enables simple and non-intrusive resource allocation and provides automatic rebalancing

Using ASM for building shared files would get almost the same performance as that of raw partitions. The ASM controlled disk devices will be part of ASM instance which can be shared by the RAC database instance. It is similar to the situation where raw devices supporting the RAC database had to be shared by multiple nodes. The shared devices need to be presented to multiple nodes on the cluster and those devices will be input to the ASM instance. There will be an ASM instance supporting each RAC instance on the respective node.

Figure 5.6 shows the files locatable on the ASM instance and files that have to come out of file system.

Figure 5.6: Using ASM instance resources for shared storage structures

As shown in the above diagram, ASM can not provide the generalized storage resources. ASM is for more Oracle specific data, redo log files, and archived log files. More detailed explanation of the ASM and its implementation method is covered in a later part of this chapter.

NFS - Network File System

NFS provides another shared storage option. Network Appliance Filers offer CFS-like functionality via NFS to the server machines. These file systems are mounted using special mount options. RAC database shared data files can be located on NFS mounts also.

And who is the winner?

From the management and maturity point, Cluster File System provides an ideal shared storage platform for all kinds of Oracle related files. Especially with the provision of Common Oracle Home, the addition of a RAC node and instance becomes relatively easy. A Large RAC cluster can be built very easily as Oracle Binaries do not need to be installed for each of the RAC instance separately. Since a single copy is maintained, it becomes easy to administer and maintain.

CFS is widely used and many stable products are available. Such examples include, HP?s Tru64 CFS, Veritas CFS and PolyServe Matrix Server. The open source product such as the OCFS (oracle cluster file system) is also widely used in Linux platforms.

The cluster file system is the most reliable and proven method of setting up the storage volumes into shareable files systems. The ease of use and flexibility of administration provided by the cluster file system has brought new interest to the RAC system. The concept, implementation, and various CFS products available for the RAC database will be examined later in this chapter.

Using the ASM based shared storage for RAC database is a recommended method by Oracle. ASM is a significant new feature in 10g release. ASM removes the management hassles of raw devices, and provides the performance advantage of the raw devices. ASM also eliminates the need for cluster file system. However, ASM is relatively new technology and it does not provide a general purpose storage platform. ASM offers better management and tuning of I/O activity.  ASM also eliminates the need for any volume management.

Next, how the physical storage array is managed and presented to the host will be examined. Hardware redundancy and design issues will also be explored.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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