Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

Database administrators can choose the datafile type used with the Oracle product.

Historically, choosing between file system files and raw devices was based on

manageability and performance. The exception to this is a database intended for

use with Oracle Parallel Server, which requires raw devices on most platforms. If

performance is not as important as administrative ease, file system files are

typically the preferred file type. However, while an application may not have

substantial I/O requirements when it is first implemented, I/O requirements may

change. If an application becomes dependent upon I/O throughput, converting

datafiles from file system to raw devices is often necessary.

Oracle Disk Manager was designed to work with Oracle10g or later to provide

both performance and manageability. Oracle Disk Manager provides support for

Oracle's file management and I/O calls for database storage on VxFS file systems

and on raw volumes or partitions. This feature is provided as a dynamically-loaded

shared library with which Oracle binds when it is loaded. The Oracle Disk Manager

library works with an Oracle Disk Manager driver that is loaded in the kernel to

perform its functions.

If you are upgrading to Oracle10g or later, you should convert from Quick I/O to

Oracle Disk Manager.

The benefits of using Oracle Disk Manager are as follows:

■ True kernel asynchronous I/O for files and raw devices

■ Reduced system call overhead

■ Improved file system layout by preallocating contiguous files on a VxFS file

system

■ Performance on file system files that is equivalent to raw devices

■ Transparent to users

For more information on using Oracle Disk Manager:

See Veritas Storage Foundation: Storage and Availability Management for Oracle

Databases.

About Cached ODM

ODM I/O normally bypasses the file system cache and directly reads from and

writes to disk. Cached ODM enables some I/O to use caching and read ahead, which

can improve ODM I/O performance. Cached ODM performs a conditional form of

caching that is based on per-I/O hints from Oracle. The hints indicate what Oracle

will do with the data. ODM uses these hints to perform caching and read ahead

for some reads, but ODM avoids caching other reads, even for the same file.

For more information on using Cached ODM:

Overview of database accelerators

About Cached ODM