Veritas File System 5.0 Administrator's Guide (September 2006)
unnecessarily serialize I/O operations. Quick I/O bypasses file system locking and
lets the database server control data access.
About double buffering avoidance
Most database servers implement their own buffer cache and do not need the
system buffer cache. Thus, the memory used by the system buffer cache is wasted
and results in data being cached twice: first in the database cache and then in the
system buffer cache. By using direct I/O, Quick I/O does not waste memory on
double buffering. This frees up memory that can then be used by the database
server buffer cache, leading to increased performance.
About using Veritas File System files as raw character
devices
When VxFS with Quick I/O is installed, files may be accessed by the following
ways:
■ 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
Quick I/O allows a database server to use the Quick I/O interface while a backup
server uses the VxFS interface.
About the 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:
The cdev portion is an acronym for character device. Whenever an application
opens an existing VxFS file with the suffix ::cdev:vxfs, 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:
185Quick I/O for Databases
About using Veritas File System files as raw character devices