Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

How Concurrent I/O works
Traditionally, UNIX semantics require that read and write operations on a file
occur in a serialized order. Because of this, a file system must enforce strict
ordering of overlapping read and write operations. However, databases do not
usually require this level of control and implement concurrency control internally,
without using a file system for order enforcement.
The Veritas Concurrent I/O feature removes these semantics from the read and
write operations for databases and other applications that do not require
serialization.
The benefits of using Concurrent I/O are:
■ Concurrency between a single writer and multiple readers
■ Concurrency among multiple writers
■ Minimalization of serialization for extending writes
■ All I/Os are direct and do not use file system caching
■ I/O requests are sent directly to file systems
■ Inode locking is avoided
■ Concurrent I/O can be used for control files, temporary datafiles, and archive
logs
Oracle's filesystemio_options parameter
In Oracle9 Release 2 (9.2), you can use the filesystemio_optionsinit.ora
parameter to enable or disable asynchronous I/O, direct I/O, or Concurrent I/O
on file system files. This parameter is used on files that reside in non-VxFS
filesystems only. This parameter is not applicable to VxFS files, ODM files, or
Quick I/O files.
See your Oracle documentation for more details.
Enabling and disabling Concurrent I/O
Concurrent I/O is not turned on by default and must be enabled manually. You
will also have to manually disable Concurrent I/O if you choose not to use it in
the future.
Using Veritas Concurrent I/O
Enabling and disabling Concurrent I/O
116