VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 8

Quick I/O for Databases

Using VxFS Files as Raw Character Devices

When VxFS with Quick I/O is installed, there are two ways of accessing a file:

• The VxFS interface treats the file as a regular VxFS file

• The Quick I/O interface treats the same file as if it were a raw character device, having performance

similar to a raw device

This allows a database server to use the Quick I/O interface while a backup server uses the VxFS interface.

Quick I/O Naming Convention

To treat a file as a raw character device, Quick I/O requires a file name extension to create an alias for a

regular VxFS file. Quick I/O recognizes the alias when you add the following suffix to a file name:

::cdev:vxfs:

Whenever an application opens an existing VxFS file with the suffix ::cdev:vxfs (the cdev portion is an

acronym for character device), Quick I/O treats the file as if it were a raw device. For example, if the file

xxx

a regular VxFS file, then an application can access

xxx

as a raw character device by opening it with the name:

xxx::cdev:vxfs:

NOTE When Quick I/O is enabled, you cannot create a regular VxFS file with a name that uses the

::cdev:vxfs: extension. If an application tries to create a regular file named

xxx::cdev:vxfs:, the create fails. If Quick I/O is not available, it is possible to create a

regular file with the ::cdev:vxfs: extension, but this could cause problems if Quick I/O is

later enabled. It is advisable to reserve the extension only for Quick I/O files.

Use Restrictions

There are restrictions to using regular VxFS files as Quick I/O files.

Step 1. The name

xxx

::cdev:vxfs: is recognized as a special name by VxFS only when:

a. VxFS with Quick I/O has a valid license

b. the regular file

xxx

is physically present on the VxFS file system

c. there is no regular file named

xxx

::cdev:vxfs: on the system

Step 2. If the file

xxx

is being used for memory mapped I/O, it cannot be accessed as a Quick I/O file.

Step 3. An I/O fails if the file

xxx

has a logical hole and the I/O is done to that hole on

xxx

::cdev:vxfs:.

Step 4. The size of the file cannot be extended by writes through the Quick I/O interface.