raw -q /dev/raw/raw
raw is used to bind a Linux raw character device to a block device. Any block device may be used: at the time of binding, the device driver does not even have to be accessible (it may be loaded on demand as a kernel module later).
raw is used in two modes: it either sets raw device bindings, or it queries existing bindings. When setting a raw device, /dev/raw/raw is the device name of an existing raw device node in the filesystem. The block device to which it is to be bound can be specified either in terms of its major and minor device numbers, or as a path name /dev/ to an existing block device file.
The bindings already in existence can be queried with the -q option, with is used either with a raw device filename to query that one device, or with the -a option to query all bound raw devices.
Once bound to a block device, a raw device can be opened, read and written, just like the block device it is bound to. However, the raw device does not behave exactly like the block device. In particular, access to the raw device bypasses the kernel's block buffer cache entirely: all I/O is done directly to and from the address space of the process performing the I/O. If the underlying block device driver can support DMA, then no data copying at all is required to complete the I/O.
Set query mode. raw will query an existing binding instead of setting a new one.
With -q , specifies that all bound raw devices should be queried.
The Linux dd (1) command does not currently align its buffers correctly, and so cannot be used on raw devices.