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 is 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.
- The name xxx::cdev:vxfs: is recognized as a special name by VxFS only when:
- VxFS with Quick I/O has a valid license
- the regular file xxx is physically present on the VxFS file system
- there is no regular file named xxx::cdev:vxfs: on the system
- If the file xxx is being used for memory mapped I/O, it cannot be accessed as a Quick I/O file.
- 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:.
- The size of the file cannot be extended by writes through the Quick I/O interface.
|
