Veritas Storage Foundation 5.0 for Oracle RAC Configuration Guide Extracts for HP Serviceguard Storage Management Suite, Second Edition, May 2008

Introducing Serviceguard Extension for RAC

Oracle Disk Manager

Chapter 1

Oracle Disk Manager

SGeRAC requires Oracle Disk Manager (ODM), a standard API published by Oracle for

support of database I/O. SGeRAC provides a library for Oracle to use as its I/O library.

ODM Architecture

When the 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 SGeRAC

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.

ODM Performance Enhancements

ODM enables the 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

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 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.