View source for Raw device

{{Short description|Special kind of logical device to allow storage device to be accessed directly}}
In [[computing]], specifically in [[Unix]] and [[Unix-like]] operating systems, a '''raw device''' is a special kind of logical device associated with a character [[device file]] that allows a storage device such as a [[hard disk drive]] to be accessed directly, bypassing the operating system's [[Page cache|caches]] and buffers (although the hardware caches might still be used). Applications like a [[database management system]] can use raw devices directly, enabling them to manage how data is cached, rather than deferring this task to the operating system.

In [[FreeBSD]], all device files are in fact raw devices.  Support for non-raw devices was removed in FreeBSD&nbsp;4.0 in order to simplify buffer management and increase scalability and performance.<ref>{{cite web
| title=FreeBSD Architecture Handbook: 9.4. Block Devices (Are Gone)
| url=https://www.freebsd.org/doc/en/books/arch-handbook/driverbasics-block.html
| access-date=2017-06-29}}</ref>

In [[Linux]], opening a block device with the {{Mono|O_DIRECT}} flag replaces raw device usage. Raw devices were removed entirely from the [[Linux kernel]] in the 5.14 release.<ref>{{cite web
| url=https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=603e4922f1c81fc2ed3a87b4f91a8d3aafc7e093
| title=remove the raw driver
| first=Christoph
| last=Hellwig
| date=2021-05-31 
| access-date=2024-07-29}}</ref>  

== References ==
{{Reflist}}

{{Linux kernel}}
{{Linux}}
{{Unix}}

[[Category:Unix file system technology]]
[[Category:Linux kernel features]]


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