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Storage Design and Redundancy

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%.

Oracle related files and directories mentioned in earlier sections reside on raw partitions or on a cluster file system or in the ASM instance. Raw partitions are a set of unformatted devices on a shared disk sub-system. The RAC shared storage files can be stored on the cluster file system wherever it is available. Disk Devices can also be placed under the control of ASM instance and make it available for the use of RAC database.

There are other file systems such as Oracle Home for the Oracle executables, the file system where the archive logs are written, and the file system where Oracle log files and trace files are written. These file systems are usually mounted on the storage volumes from either the local storage or cluster file system.

Figure 5.7: Shared Storage supporting multiple instances

As shown in Figure 5.7, the storage system is the key component for both the survival of the database system and for its high availability. For example, this diagram shows a 6-node cluster with a very reliable architecture comprised of powerful processors, a large memory in each server, and all 6-nodes sharing the storage system. The 6 nodes jointly provide both the parallel computing environment and high availability. Imagine a storage unit was lost and all 6-nodes are still functioning, but cannot provide the database service. The storage unit is the Achilles Heel. Thus the storage occupies an important place in the overall architecture of the RAC system. It is crucial to plan and design carefully to get the right storage array in a compatible environment.

There are a number of methods used to access the information on the storage systems in the information infrastructure. They include Direct Attached Storage (DAS), Network Attached Storage (NAS), and the Storage Area Networks (SAN). These technologies are not mutually exclusive. Instead, they are complementary.

The inherent advantages of networked storage have been responsible for the gradual replacement of the DAS storage model. According to a recent report by International Data Corp. (IDC), networked storage will account for 67% of disk storage systems by 2005.

The database servers are able to store and access the data from all of these models. When implementing database servers with the clustered server architecture it is advisable to use a storage model that provides a very reliable and highly available platform. In the case of the Oracle RAC system, clustering protects the servers (or hosts) but the shared storage system still requires a suitable protection method.

Storage Disk System

The past decade has seen many changes in disk subsystem technology. The power and intelligence of the storage system has improved considerably. These are no longer dumb disk drives. They are now equipped with intelligent RAID controllers, large cache buffers, and smart switches to control the multiple servers? access, to name just a few. Much of the RAID functionality is confined within the storage unit, thus saving CPU server cycles for other uses as well as eliminating the complexity of software RAID administration.

Some of the storage models and components will be reviewed next.

Just a Bunch of Disks (JBOD)

Just a Bunch of Disks (JBOD) is a simple disk subsystem that provides disk media and I/O connectivity for multiple disk drives located in an external cabinet. JBOD disk drives are individually accessed by the host system and are mirrored/striped and formed into usable volumes at the host level, usually with the help of the logical volume manager (software RAID).

Thus, the host-controlled RAID is used to provide the redundancy. There are many server systems that employ this kind of architecture, but they are becoming less frequent with the wide availability of more intelligent storage arrays. Moreover, the historical disparity in cost between JBOD and intelligent storage is decreasing.


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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