Oracle Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 8 - RAC Administration

Oracle Disk Manager

Oracle disk manager (ODM) is a disk management interface defined by Oracle to enhance file management and disk I/O performance. Implementation of an ODM interface in a file system or a logical volume manager (LVM) provides many benefits including simplified file administration, improved file integrity, and reduced system overhead. It is completely transparent from an application/DBA perspective. It is an improvement over standard Unix I/O.

ODM eliminates file descriptors, which simplifies the operating system kernel configuration and saves operating system resources. Other ODM capabilities include special locking modes that prevent errors and the ability to pass usage hints, such as Oracle file type information and I/O priorities for third party application integration. It manages all I/O type files on both system files and raw partitions with one system call, which is not possible with native operating system calls.

Some of the visible advantages include:

• Files being created/initialized are not visible until they are 'committed'.
   

• Files must be identified (opened) with a common 'key' and cannot be removed if they are in use.
   

• Works with regular files and raw volumes.

Oracle Database 10g automatically takes advantage of the ODM interface when the underlying file system or logical volume manager becomes ODM enabled. A file is considered an ODM file if it is in a file system that supports the ODM interface. ODM is also compatible with the new Oracle Real Application Clusters.