Installation guide

Systems which are not running multipath must use Single path configuration. Systems running
multipath can use Multiple path configuration.
Sin g le pat h co n f ig u rat io n
This procedure implements LUN device persistence using udev. Only use this procedure for hosts
which are not using multipath.
1. Edit the /etc/scsi_id.config file.
a. Ensure the options=-b is line commented out.
# options=-b
b. Add the following line:
options=-g
This option configures udev to assume all attached SCSI devices return a UUID.
2. To display the UUID for a given device run the scsi_id -g -s /block/sd* command.
For example:
# scsi_id -g -s /block/sd*
3600a0b800013275100000015427b625e
The output may vary from the example above. The output displays the UUID of the device
/dev/sdc.
3. Verify the UUID output by the scsi_id -g -s /block/sd* command is identical from
computer which accesses the device.
4. Create a rule to name the device. Create a file named 20-names.rules in the
/etc/udev/rules.d directory. Add new rules to this file. All rules are added to the same file
using the same format. Rules follow this format:
KERNEL=="sd[a-z]", BUS=="scsi", PROGRAM="/sbin/scsi_id -g -s /block/%k",
RESULT="UUID", NAME="devicename"
Replace UUID and devicename with the UUID retrieved above, and a name for the device. This
is a rule for the example above:
KERNEL="sd*", BUS="scsi", PROGRAM="/sbin/scsi_id -g -s",
RESULT="3600a0b800013275100000015427b625e", NAME="rack4row16"
The udev daemon now searches all devices named /dev/sd* for the UUID in the rule. Once
a matching device is connected to the system the device is assigned the name from the rule.
In the a device with a UUID of 3600a0b800013275100000015427b625e would appear as
/dev/rack4row16.
5. Append this line to /etc/rc.local:
/sbin/start_udev
6. Copy the changes in the /etc/scsi_id.config, /etc/udev/rules.d/20-
names.rules, and /etc/rc.local files to all relevant hosts.
Red Hat En t erp rise Lin ux 5 Virt ualizat ion Guid e
134