How do I add raw device mapping in
Red Hat Enterprise Linux 5
Issue
How do I add raw device mapping in Red Hat Enterprise Linux
5?
Environment
- Red
Hat Enterprise Linux 5
- raw
device
Resolution
Previously (Red Hat Enterprise Linux 5.0 through Red Hat
Enterprise Linux 5.3), support for raw devices in the upstream kernel was
deprecated. However, this support has been returned to the kernel.
Consequently, in Red Hat Enterprise Linux 5.4, support for raw devices has also
been returned. Additionally, the initscripts packages have been updated, adding
the previously dropped functionality of raw devices.
So in the Red Hat Enterprise Linux 5, there are two methods
to configure RAW device.
Method 1. Using rawdevices service (Not available on
RHEL5.0 -- RHEL5.3)
1. Edit the file /etc/sysconfig/rawdevices
service rawdevices
start
# raw device
bindings
# format: <rawdev> <major> <minor>
# <rawdev> <blockdev>
# example: /dev/raw/raw1
/dev/sda1
# /dev/raw/raw2 8 5
/dev/raw/raw1
/dev/hda5
/dev/raw/raw2
/dev/hda6
(Notes: /dev/raw/raw0 is not allowed because minor number
cannot be zero.)
2. Start the rawdevices service
#service
rawdevices start
#chkconfig
rawdevices on
Method 2. Using udev to configure RAW device
1. Creating the raw devices using udev:
Nevertheless, to create raw devices, add entries to
/etc/udev/rules.d/60-raw.rules in the following formats:
For device names:
ACTION=="add", KERNEL=="<device
name>", RUN+="raw /dev/raw/rawX %N"
For major / minor numbers:
ACTION=="add", ENV{MAJOR}=="A",
ENV{MINOR}=="B", RUN+="raw /dev/raw/rawX %M %m"
Note: Replace <device name> with the name
of the device needed to bind (such as /dev/sda1). "A" and "B"
are the major / minor numbers of the device needed for binding, an
"X" is the raw device number that the system wants to use.
2. Creating persistent raw devices for single path
LUNs:
If using unpartitioned LUNs, to create a single raw device for the whole LUN
use this rule format:
ACTION=="add", KERNEL=="sd*[!0-9]",
PROGRAM=="/sbin/scsi_id -g -u -s %p",
RESULT=="3600601601bd2180072193a9242c3dc11", RUN+="/bin/raw
/dev/raw/raw1 %N"
Note: Set the RESULT value to the output of
scsi_id -g -u -s /block/sdX (where sdX is the current path to the LUN). This
will create the raw device /dev/raw/raw1 that will be persistently bound to the
LUN with WWID 3600601601bd2180072193a9242c3dc11.
If using partitioned LUNs, where raw devices are created for
each of the partitions on the LUN, use this rule format:
ACTION=="add",
KERNEL=="sd*[0-9]", PROGRAM=="/sbin/scsi_id -g -u -s %p",
RESULT=="3600601601bd2180072193a9242c3dc11", RUN+="/bin/raw
/dev/raw/raw%n %N"
Again
, set RESULT to the output of scsi_id -g -u -s /block/sdX.
This will create the raw device(s) /dev/raw/raw1, /dev/raw/raw2, etc. for each
partition on the LUN and they will be persistently bound to the LUN with WWID
3600601601bd2180072193a9242c3dc11.
3. Setting ownership and permissions on the raw
devices:
To set specific ownership and/or permissions for the raw
devices, add entries to /etc/udev/rules.d/60-raw.rules in the following format:
ACTION=="add",
KERNEL=="raw*", OWNER="root", GROUP="disk",
MODE="0660"
4. Testing and implementing the udev rules:
Before implementing them, use the udevtest command to verify
the udev rules work as expected. To verify that the raw device is created for a
specific disk or partition, eg /dev/sdb1:
[root@rhel5 rules.d]#
udevtest /block/sdb/sdb1 | grep raw
main: run: '/bin/raw
/dev/raw/raw1 /dev/.tmp-8-17'
To check ownership/permission settings for a particular raw
device, eg /dev/raw/raw1:
[root@rhel5 rules.d]#
udevtest /class/raw/raw1 | grep mode
udev_node_add:
creating device node '/dev/raw/raw1', major = '162', minor = '1', mode =
'0600', uid = '0', gid = '0'
Finally, to actually create the raw device(s), use the
start_udev command:
[root@rhel5 rules.d]#
start_udev
Starting udev:
[ OK ]
Check that the raw device(s) have been created:
[root@rhel5 rules.d]#
raw -qa
/dev/raw/raw1: bound to major 8, minor 17
[root@rhel5 rules.d]#
ls -l /dev/raw
total 0
crw-rw---- 1
root disk 162, 1 Jan 29 02:47 raw1
5. Creating persistent raw devices for multipathed LUNs
or LVM device:
Unfortunately it is not possible to write udev rules for
creating raw devices on multipath devices (/dev/dm-*) without manipulating
existing udev rules. Modifying existing rules for this purpose could cause
unforeseen problems and is not supported by Red Hat Global Support Services. If
absolutely necessary, an alternate method for creating raw devices on top of
multipath devices could be to create the raw devices in /etc/rc.d/rc.local, so
long as the raw device is not required before rc.local is executed. For
example:
/bin/raw
/dev/raw/raw1 /dev/mpath/mpath1p1
/bin/raw
/dev/raw/raw2 /dev/mpath/mpath1p2
/bin/chmod 660
/dev/raw/raw1
/bin/chown root:disk
/dev/raw/raw1
/bin/chmod 660
/dev/raw/raw2
/bin/chown root:disk
/dev/raw/raw2
If absolutely want to create raw devices for multipathed
LUNs or LVM device using udev, can add the following udev rules in the
file /etc/udev/rules.d/60-raw.rules
# Device mapper raw rules
KERNEL!="dm-[0-9]*", GOTO="skip_dm"
ACTION!="change", GOTO="skip_dm"
PROGRAM!="/sbin/dmsetup ls --exec /bin/basename -j %M
-m %m", GOTO="skip_dm"
RESULT=="mpath2", RUN+="/bin/raw
/dev/raw/raw2 /dev/mapper/mpath2"
RESULT=="mpath1", RUN+="/bin/raw
/dev/raw/raw1 /dev/mapper/mpath1"
LABEL="skip_dm"
KERNEL=="raw1", ACTION=="add",
OWNER="root", GROUP="disk", MODE="0660"
KERNEL=="raw2", ACTION=="add",
OWNER="root", GROUP="disk", MODE="0660"
Note: The first three rules makes sure we are
only using dm devices with change actions, when dmsetup returns success. If
not, we skip down to the "skip_dm" label. After that, the rules
look at the result of running dmsetup, and do fire off the appropriate command.
