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10g Grid Computing with RAC
Preparing Shared Storage

Shared Storage

This article will cover preparing shared storage structures. Shared storage is the main and critical requirement for building and managing the RAC database.

Whatever the number of nodes and database instances we may have in the RAC, all of them will have shared access to the underlying storage. Setting up shared storage, creating the hardware level structures, provisioning of the adequate storage redundancy and preparation of host level storage logical storage units are very important. For setting up the needed shared storage structures at the host level for the RAC database, there are more options. These options use shared storage in terms of cluster file system, raw devices and Oracle’s Automated Storage Management (ASM).

 Being a shared architecture, RAC system’s shared storage is a crucial component overall design and well being.

The relational database system is basically a logical entity that stores and retrieves organized data. The database resides in the storage structures and provides a front end for the data’s use. Thus, the database enjoys a very close connection with the storage units. Channels or paths connect the storage units with the servers and server components. The server, being the main abode of the database system, must have many robust features to provide continuous service. As shown in Fig. 5.1, there are multiple layers in the infrastructure. At the core are the storage units. The storage logical units (LUNS) are presented to the server layer and are usually available for use as raw volumes, as mounted (cluster) file systems and as the ASM  (automatic storage management) resources.

Figure 5.1 Storage Units and other system layers

The next layer consists of the server. Even without clustering, the server has to be designed with robust components. There should be a sense of local resiliency. When one of the components falters, there should be a backup or standby component to provide the desired functionality. The cluster layer lies outside the server layer and deals with the loss of the server by failing over to a backup or standby server. Finally, the outside layer is subject to environmental problems such as client connectivity and network failures, which cause bottlenecks between the client and the database.

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