Raw device

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In computing, specifically Linux, a raw device is a special kind of block device file that allows accessing a storage device such as a hard drive directly, bypassing the operating system's 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.

On Linux raw devices are deprecated and scheduled for removal, because the O_DIRECT flag can be used instead.[1] Instead of accessing a special raw device file, the application simply can (and should!) access a file with the O_DIRECT flag enabled, and caching will be disabled. Since there is still a userbase for raw devices and applications without support for O_DIRECT still exist, it has been a controversial subject on the Linux kernel mailing list.