Basics Of Raw Devices - Red Hat ENTERPRISE LINUX 5.1 - LINUX ORACLE Tuning Manual

Chapter 13. Configuring I/O for Raw Partitions
the alias settings in this example would not be required in Red Hat Enterprise Linux 4
and 5. For more information, see
careful when adding/removing devices which can change device names on the system.
Starting Oracle with incorrect device names or raw devices can cause permanent damage
to the database. For stable device naming in Linux 2.4 and 2.6, see

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:
# 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
# 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:
/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:
/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:
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:
/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:
38
Red Hat Enterprise Linux AS 4 Release Notes
1
. Be also
2
Optimizing Linux I/O
.