Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.1, Tuning Manual

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Chapter 13. Configuring I/O for Raw Partitions
38
the alias settings in this example would not be required in Red Hat Enterprise Linux 4
and 5. For more information, see
Red Hat Enterprise Linux AS 4 Release Notes
1
. Be also
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
Optimizing Linux I/O
2
.
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: