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The Voting Disk File

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%.


The Voting Disk File is a file on the shared cluster system or a shared raw device file. Voting disk is akin to the quorum disk which helps to avoid the split brain syndrome.

ORACLE_HOME Files (Oracle Binaries)

Typically every instance in the RAC database system will have its own ORACLE HOME and a set of exclusive binaries. However, the Oracle Binaries are located either on a local file system or on a clustered file system. Locating the Oracle Home (Binaries) on a clustered file system provides easier management by keeping a single copy of Oracle Home supporting all the instances.

Common Oracle Home for multiple instances is an attractive proposition as it helps to easily expand the nodes and shrink the nodes as needed. It helps the dynamic addition and expansion of nodes without bothering with a fresh install of the Oracle binaries for the new instance. This feature is particularly useful for large clusters and it fits into the Grid strategy of easier addition and reduction of computing resources.

UNDO Tablespace Files

UNDO tablespace are special tablespaces that have system undo segments. They contain before images of blocks involved in uncommitted transactions. As such, they are the primary support structure allowing a transaction to rollback if the decision is made to not commit the transaction. These tablespaces also support the Oracle functionality known as Multi-block Read Consistency. If configured to use System Managed Undo, there must be one UNDO tablespace available for each instance in the RAC setup. With 10g, this is the only method. The earlier system of public or private rollback segments is discontinued.

RAW Partitions, Cluster File System and Automatic Storage Management (ASM)

Each of the above mentioned structures are either on raw partitions or on a cluster file system. 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.

Oracle RAC database files are located on the shared storage units. Shared storage disks are physically connected to all the nodes. All the nodes need to have read and write access concurrently to the data devices. The presentation of the data devices to the operating systems can be achieved by either raw partitions or through the cluster file system. A raw partition is a disk drive device that does not have a file system set up. The raw partition is a portion of the physical disk that is accessed at the lowest possible level. The actual application that uses a raw device is responsible for managing its own I/O to the raw device with no operating system buffering.

Traditionally, they were required for Oracle Parallel Server (OPS) and provided high performance by bypassing the file system overhead. Raw partitions were used in setting up databases for performance gains and for the purpose of concurrent access by multiple nodes in the cluster without system-level buffering. Oracle9i RAC and 10g now support both the cluster file systems and the raw devices to store shared data. In addition, 10g RAC supports shared storage resources from Automatic Storage Management (ASM) instance. The data files can be created out of the disk resources located in the ASM instance. The ASM resources are sharable and accessed by all the nodes in the RAC system.

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. More details and how to prepare the file structures are covered in Chapter 5, Preparing Shared Storage.

 


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.

http://www.rampant-books.com/book_2004_1_10g_grid.htm


 

 
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