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Oracle Disk Manager

SF Oracle RAC requires Oracle Disk Manager (ODM), a standard API published by Oracle for support of database I/O. SF Oracle RAC provides a library for Oracle to use as its I/O library.

ODM architecture

When the Veritas ODM library is linked, Oracle is able to bypass all caching and locks at the file system layer and to communicate directly with raw volumes. The SF Oracle RAC implementation of ODM generates performance equivalent to performance with raw devices while the storage uses easy-to-manage file systems.

All ODM features can operate in a cluster environment. Nodes communicate with each other before performing any operation that could potentially affect another node. For example, before creating a new data file with a specific name, ODM checks with other nodes to see if the file name is already in use.

Veritas ODM performance enhancements

Veritas ODM enables performance benefits provided by Oracle Disk Manager:

• Locking for data integrity.
• Few system calls and context switches.
• Increased I/O parallelism.
• Efficient file creation and disk allocation.

Databases using file systems typically incur additional overhead:

• Extra CPU and memory usage to read data from underlying disks to the file system cache. This scenario requires copying data from the file system cache to the Oracle cache.
• File locking that allows for only a single writer at a time. Allowing Oracle to perform locking allows for finer granularity of locking at the row level.
• File systems generally go through a standard Sync I/O library when performing I/O. Oracle can make use of Kernel Async I/O libraries (KAIO) with raw devices to improve performance.

ODM communication - Port d

ODM uses port d to communicate with other ODM instances to support the file management features of Oracle Managed Files (OMF). OMF enables DBAs to set database parameters, such as the init.ora parameters for db datafile, controlfile, and logfile names, and for those structures to be named automatically. OMF allows for the automatic deletion of physical data files when DBAs remove tablespaces.