Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

and whether or not the file is in use by the database. OMF is only supported for
databases that reside in file systems. OMF functionality is greatly enhanced by
Oracle Disk Manager.
OMF is a file management feature that:
■ Eliminates the task of providing unique file names
■ Offers dynamic space management by way of the tablespace auto-extend
functionality of Oracle10g or later
The main requirement for OMF is that the database be placed in file system files.
There are additional prerequisites imposed upon the file system itself.
OMF should only be used in file systems that reside within striped logical volumes,
which support dynamic file system growth. File systems intended for OMF use
must also support large, extensible files in order to facilitate tablespace
auto-extension. Raw partitions cannot be used for OMF.
By default, OMF datafiles are created with auto-extensibility. This attribute reduces
capacity planning associated with maintaining existing databases and
implementing new applications. Due to disk fragmentation that occurs as the
tablespace grows over time, database administrators have been somewhat cautious
when considering auto-extensible tablespaces. Oracle Disk Manager eliminates
this concern.
When Oracle Disk Manager is used in conjunction with OMF, special care is given
within Veritas Extension for Disk Manager to ensure that contiguous disk space
is allocated to datafiles, including space allocated to a tablespace when it is
auto-extended. The table and index scan throughput does not decay as the
tablespace grows.
How Oracle Disk Manager works with Oracle Managed Files
The following example illustrates the relationship between Oracle Disk Manager
and Oracle Managed Files (OMF). The example shows the init.ora contents and
the command for starting the database instance. To simplify Oracle UNDO
management, the new Oracle10g or later init.ora parameter UNDO_MANAGEMENT
is set to AUTO. This is known as System-Managed Undo.
Note: Before building an OMF database, you need the appropriate init.ora default
values. These values control the location of the SYSTEM tablespace, online redo
logs, and control files after the CREATE DATABASE statement is executed.
$ cat initPROD.ora
UNDO_MANAGEMENT = AUTO
109Using Veritas Extension for Oracle Disk Manager
About Oracle Disk Manager and Oracle Managed Files