13.2. Basics of Raw Devices

To bind the first raw device /dev/raw/raw1 to the /dev/sdz SCSI disk or LUN you can execute the following command:

Copy to Clipboard Toggle word wrap

raw /dev/raw/raw1 /dev/sdz

# raw /dev/raw/raw1 /dev/sdz

Now when you run the dd command on /dev/raw/raw1, it will write directly to /dev/sdz bypassing the OS block buffer cache:

Warning

The following command will overwrite data on dev/sdz

Copy to Clipboard Toggle word wrap

dd if=/dev/zero of=/dev/sdz count=1

# dd if=/dev/zero of=/dev/sdz count=1

To permanently bind /dev/raw/raw1 to /dev/sdz, add an entry to the /etc/sysconfig/rawdevices file:

Copy to Clipboard Toggle word wrap

/dev/raw/raw1 /dev/sdz

/dev/raw/raw1 /dev/sdz

Now when you run /etc/init.d/rawdevices it will read the /etc/sysconfig/rawdevices file and execute the raw command for each entry:

Copy to Clipboard Toggle word wrap

/etc/init.d/rawdevices start

/etc/init.d/rawdevices start

To have /etc/init.d/rawdevices run each time the system boot, it can be activated by executing the following command:

Copy to Clipboard Toggle word wrap

chkconfig rawdevices on

chkconfig rawdevices on

Note

For each block device you need to use another raw device.

To bind the third raw device to the second partition of /dev/sdz, the entry in /etc/sysconfig/rawdevices would look like this:

Copy to Clipboard Toggle word wrap

/dev/raw/raw3 /dev/sdz2

/dev/raw/raw3 /dev/sdz2

Or to bind the 100th raw device to /dev/sdz, the entry in /etc/sysconfig/rawdevices would look like this:

Copy to Clipboard Toggle word wrap

/dev/raw/raw100 /dev/sdz

/dev/raw/raw100 /dev/sdz