Tasks for setting up Quick I/O in a database environment


Tasks for setting up Quick I/O in a database environment
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Quick I/O is included in the VxFS package shipped with Veritas InfoScale Storage Foundation Standard and Enterprise products. By default, Quick I/O is enabled when you mount a VxFS file system.

If Quick I/O is not available in the kernel, or a Veritas InfoScale Storage or Veritas InfoScale Enterprise product license is not installed, a file system mounts without Quick I/O by default, the Quick I/O file name is treated as a regular file, and no error message is displayed. If, however, you specify the -o qio option, the mount command prints the following error message and terminates without mounting the file system.

	VxFDD: You don't have a license to run this program
	vxfs mount: Quick I/O not available

To use Quick I/O, you must:

Preallocate files on a VxFS file system

Preallocating database files for Quick I/O allocates contiguous space for the files. The file system space reservation algorithms attempt to allocate space for an entire file as a single contiguous extent. When this is not possible due to lack of contiguous space on the file system, the file is created as a series of direct extents. Accessing a file using direct extents is inherently faster than accessing the same data using indirect extents. Internal tests have shown performance degradation in OLTP throughput when using indirect extent access. In addition, this type of preallocation causes no fragmentation of the file system.

You must preallocate Quick I/O files because they cannot be extended through writes using their Quick I/O interfaces. They are initially limited to the maximum size you specify at the time of creation.

Use a special file naming convention to access the files

VxFS uses a special naming convention to recognize and access Quick I/O files as raw character devices. VxFS recognizes the file when you add the following extension to a file name:

::cdev:vxfs:

Whenever an application opens an existing VxFS file with the extension ::cdev:vxfs: (cdev being an acronym for character device), the file is treated as if it were a raw device. For example, if the file temp01 is a regular VxFS file, then an application can access temp01 as a raw character device by opening it with the name:

.temp01::cdev:vxfs:

Note:

We recommend reserving the ::cdev:vxfs: extension only for Quick I/O files. If you are not using Quick I/O, you could technically create a regular file with this extension; however, doing so can cause problems if you later enable Quick I/O.

Depending on whether you are creating a new database or are converting an existing database to use Quick I/O, you have the following options:

If you are creating a new database to use Quick I/O:

You can use the qiomkfile command to preallocate space for database files and make them accessible to the Quick I/O interface.
You can use the setext command to preallocate space for database files and create the Quick I/O files.

If you are converting an existing database:

You can create symbolic links for existing VxFS files, and use these symbolic links to access the files as Quick I/O files.

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