Oracle Tips by Burleson

10g Grid Computing with RAC
Preparing Shared Storage

Storage Design and Redundancy

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 the 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 we can see in Fig. 5.7, the storage system is the key component for both the survival of the database system and for its high availability. For example, we have 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 we have lost the storage unit for whatever reason 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 we implement the database servers with the clustered server architecture, we should 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.

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