Veritas Storage Foundation 5.1 SP1: Storage and Availability Management for Oracle (5900-1504, April 2011)

Using Oracle's AUTOEXTEND with Quick I/O files
Oracle supports an automatic extend feature that automatically grows a database
file by a prespecified amount, up to a prespecified maximum size.
For regular file system files, AUTOEXTEND works transparently, provided the
underlying file system has enough space. For example, suppose the current size
of a database file emp.dbf is 100MB, but this file is expected to triple in size over
time. To accommodate this growth using AUTOEXTEND feature, you can specify the
next size at 20MB and maxsize at 300MB. This will automatically grow the file
by 20MB until its size reaches 300MB. For example:
alter database datafile ’emp.dbf’ autoextend on next 20m \
maxsize 300m;
(See the Oracle Server SQL Reference Guide for more information about the alter
database command, as well as the next and maxsize parameters.)
Note: You must have sufficient space on the underlying file system to AUTOEXTEND
a file, and the underlying storage device must be large enough to contain the new,
larger file system.
For Quick I/O files or raw devices, AUTOEXTEND does not know how to grow the
underlying Quick I/O files or devices. Therefore, the Quick I/O file size must be
large enough to accommodate the new size before AUTOEXTEND can grow the
datafile.
You can use AUTOEXTEND with Quick I/O files in the following ways:
■ Preallocate the Quick I/O file to a size at least as big as the maximum growth
size expected for this database file.
Using this method, you would need to preallocate the Quick I/O file emp.dbf
for the entire 300MB. The drawback is that this can unnecessarily lock up
excess disk space. Raw devices have a similar requirement.
■ Monitor the free space available in the Quick I/O file, and grow the file as
necessary with the qiomkfile command.
Unlike raw devices, you can easily extend Quick I/O files online. Using this
method, you can monitor the free space available in the Oracle datafiles and
use the qiomkfile command to grow the Quick I/O files online as and when
needed (typically when the file is about 80 to 90 percent full). This method
does not require you to lock out unused disk space for Quick I/O files. The free
space on the file system is available for use by other applications.
The following options are available for the qiomkfile command:
Improving database performance with Veritas Quick I/O
Using Oracle's AUTOEXTEND with Quick I/O files
104