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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:
/dev/raw/raw100 /dev/sdz
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