Raw device
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 now obsolete and have been removed from the kernel, because the O_DIRECT flag can be used instead.[1] Instead of accessing a special raw device file, the application simply accesses a file with the O_DIRECT flag enabled, and caching will be disabled.