User manual REDHAT CLUSTER SUITE 4.7 DM MULTIPATH CONFIGURATION

[. . . ] Red Hat Cluster Suite 4. 7 DM Multipath DM Multipath Configuration and Administration DM Multipath Red Hat Cluster Suite 4. 7 DM Multipath DM Multipath Configuration and Administration Edition 1. 0 Copyright © 2008 Red Hat, Inc. This material may only be distributed subject to the terms and conditions set forth in the Open Publication License, V1. 0 or later with the restrictions noted below (the latest version of the OPL is presently available at http://www. opencontent. org/openpub/). Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. Distribution of the work or derivative of the work in any standard (paper) book form for commercial purposes is prohibited unless prior permission is obtained from the copyright holder. [. . . ] Use the following procedure to set up DM-Multipath for a basic failover configuration. Edit the /etc/multipath. conf file by commenting out the following lines at the top of the file. This section of the configuration file, in its initial state, blacklists all devices. You must comment it out to enable multipathing. devnode_blacklist { devnode "*" } After commenting out those lines, this section appears as follows. # devnode_blacklist { # devnode "*" #} 2. The default settings for DM-Multipath are compiled in to the system and do not need to be explicitly set in the /etc/multipath. conf file. The default value of path_grouping_policy is set to failover, so in this example you do not need to change the default value. For information on changing the values in the configuration file to something other than the defaults, see Chapter 4, The DM-Multipath Configuration File. The initial defaults section of the configuration file configures your system that the names of the multipath devices are are of the form mpathn; without this setting, the names of the multipath devices would be aliased to the WWID of the device. Save the configuration file and exit the editor. Execute the following commands: modprobe dm-multipath service multipathd start 7 Chapter 3. Setting Up DM-Multipath multipath -v2 The multipath -v2 command prints out multipathed paths that show which devices are multipathed. If the command does not print anything out, ensure that all SAN connections are set up properly and the system is multipathed. For further information on the multipath command output, see Section 5. 1, "Multipath Command Output". Execute the following command to ensure sure that the multipath daemon starts on bootup: chkconfig multipathd on Since the value of user_friendly_name is set to yes in the configuration filea the multipath devices will be created as /dev/mapper/mpathn. For information on setting the name of the device to an alias of your choosing, see Chapter 4, The DM-Multipath Configuration File. 3. 2. Ignoring Local Disks when Generating Multipath Devices Some machines have local SCSI cards for their internal disks. DM-Multipath is not recommended for these devices. The following procedure shows how to modify the multipath configuration file to ignore the local disks when configuring multipath. Determine which disks are the internal disks and mark them as the ones to blacklist. In this example, /dev/sda is the internal disk. Note that as originally configured in the default multipath configuration file, executing the multipath -v2 shows the local disk, /dev/sda, in the multipath map. For further information on the multipath command output, see Section 5. 1, "Multipath Command Output". [root@rh4cluster1 ~]# multipath -v2 create: SIBM-ESXSST336732LC____F3ET0EP0Q000072428BX1 [size=33 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 0:0:0:0 sda 8:0 [--------device-mapper ioctl cmd 9 failed: Invalid argument device-mapper ioctl cmd 14 failed: No such device or address create: 3600a0b80001327d80000006d43621677 [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:0 sdb 8:16 \_ 3:0:0:0 sdf 8:80 create: 3600a0b80001327510000009a436215ec [size=12 GB][features="0"][hwhandler="0"] 8 Ignoring Local Disks when Generating Multipath Devices \_ round-robin 0 \_ 2:0:0:1 sdc \_ 3:0:0:1 sdg 8:32 8:96 create: 3600a0b80001327d800000070436216b3 [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:2 sdd 8:48 \_ 3:0:0:2 sdh 8:112 create: 3600a0b80001327510000009b4362163e [size=12 GB][features="0"][hwhandler="0"] \_ round-robin 0 \_ 2:0:0:3 sde 8:64 \_ 3:0:0:3 sdi 8:128 2. [. . . ] When a multipath device is being listed, the path group priority is not known. 5. 2. Multipath Queries with multipath Command You can use the -l and -ll options of the multipath command to display the current multipath configuration. The -l option displays multipath topology gathered from information in sysfs and the device mapper. The -ll option displays the information the -l displays in addition to all other available components of the system. [. . . ]