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DB Optimized Option

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%.


One important mount option that is useful for setting up the file systems for an Oracle database is DB Optimized. PolyServe specially provides the DB Optimized option for the use of database files. This option bypasses file system I/O buffering allowing disk transfers to occur directly in application buffers. This allows a database system, such as RAC, to manage its own data coherency and integrity.

To take advantage of the performance optimization, the read or write system call buffer must be aligned on a page boundary and the I/O must be 512 bytes or a multiple offset. The size of the I/O must also be 512 bytes or a multiple thereof. Oracle I/O is sized as a db_block_size operation and will always be a 512 byte multiple.

In such a case, the files in the DB Optimized file system are treated as direct I/O files, and the I/O is completely un-buffered and not serialized through any OS locking. Any access to files in a DB Optimized mounted file system that do not fit the alignment requirements do succeed ? through the buffered I/O path. Regular file system commands can be used against these files such as cp, rm, compress, etc.

DB Optimized file systems are used to store all Oracle data files, redo logs, control files, SPFILE, OCR file, and CRS voting disk.

Configure Veritas CFS for Solaris and HP platforms

Another option available for Solaris and HP platform is the use of Veritas Advance Cluster solution, which provides comprehensive cluster software and shared storage solutions. In this section, the shared storage solution will be examined in terms of the Veritas cluster file system (CFS).

Setting up volumes and making sure the cluster file system is accessible by all nodes configures the shared storage. In sum the volumes and the CFS depend on the physical storage. The cluster volume manager manages all related objects such as physical disks (LUNS), disk groups, volumes, and file systems. Oracle uses the ODM (Oracle disk manager) interface to communicate with Veritas volumes and CFS files.

Cluster Volume Manager (CVM)

CVM is basically an extension of the widely used Veritas Volume Manager. CVM extends the functionality of the VxVM to all the nodes in the cluster. Each node sees the same state of all volume resources. It follows master/slave architecture. One node usually acts as master and others as slaves. There is only one master in a given cluster. The volume manager daemon (vxconfigd) maintains the configuration of the logical volumes. Each node in the node has the vxconfigd daemon. Changes to a volume are propagated first to the master daemon and then the master passes it on to slave daemons. These changes happen at the kernel level.

CVM does not attempt to do any locking between the nodes. That is the responsibility of the application, as in the RAC database. CVM also follows the uniform shared storage model. This means that all systems must be connected to the same disk sets for a given disk group. If a node loses contact with a specific disk, it is excluded from using the disk.

Cluster File System (CFS)

Veritas CFS has evolved from the Veritas File System (VxFS). CFS allows the same file system to be simultaneously mounted on multiple nodes in the cluster. Once again, the CFS is designed with master/slave architecture. Though any node can initiate an operation to create, delete, or resize data, the master node carries out the actual operation. CFS caches the metadata in memory, typically in the memory buffer cache or the vnode cache. A distributed locking mechanism, called GLM, is used for metadata and cache coherency among the multiple nodes. However, with implementation of the ODM interface, Oracle RAC accesses data files stored on CFS, bypassing the file system buffer and file system locking processes. Oracle manages its own consistency mechanism. The ODM facility is automatically invoked with RAC.

 


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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