Most operating systems support numerous types of file systems. Some aspects of file system operation are independent of file system type and are implemented in a common part of the operating system kernel. However, many other aspects of file system operation, including direct I/O availability, are dependent on the type of file system in use. For example, some file systems cannot support direct I/O because their file system structure is such that file system blocks do not align with device block boundaries and so I/O requests cannot be mapped directly from file system blocks to device blocks. File systems that can support direct I/O may only be able to do so via a mount option if the file system independent layer of the operating system does not support a direct I/O flag in its open() system call.
The following table details the availability of program selectable direct I/O for some important operating systems. Oracle may use this operating system feature automatically when opening database files, or it may be used based on the setting of the filesystemio_options parameter. Of course, the file system must support direct I/O for that setting to be effective. See the second table below for details about which file systems support program selectable direct I/O.
|Operating system||Program selectable direct I/O|
|Solaris||available, used based on filesystemio_options|
|Windows NT/2000||available, used automatically|
|Tru64 Unix||available, used automatically from 18.104.22.168 (and in 22.214.171.124) on 5.1 with PK4|
or 5.1A with PK1 or later; can be disabled with _tru64_directio_disabled or filesystemio_options from 9.2
|AIX||available, usage unknown|
|Irix||available, usage unknown|
|Linux||available (2.4 kernels), not yet used by Oracle|
|Reliant Unix||not available|
The following table details direct I/O availability for some important file systems.
|File system||Mount option||Program selectable|
|Reliant Unix VxFS||convosync=direct||no|
|Reliant Unix UFS||none||no|
|Tru64 Unix AdvFS||none||yes|
|Tru64 Unix UFS||none||no|
If your operating system or file system is not listed in the tables above, and if you are aware of the details, please click on the feedback icon below and send us an email so that we can add it to the list.
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