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MPATH_PRIO_ALUA(8) Linux Administrator's Manual MPATH_PRIO_ALUA(8) NAME mpath_prio_alua - Path priority tool based on Asymmetric LUn Access SYNOPSIS mpath_prio_alua [-d directory] [-h] [-v] [-V] device [ device [ ... ]] DESCRIPTION mpath_prio_alua is used as a priority callout for the multipath com- mand. It returns a number that is used by multipath to group devices with the same priority together. OPTIONS -d directory target directory for devices given as relative device names or devices given as major:minor number. Default is "/dev". -h displays the command line help. -v turns on verbose output. This shows all results in human read- able format. This includes information about the port group the device is in and its current state. -V shows the version number and exits. device specifies the device to query (the device must be a SCSI device that supports the "Report Target Port Groups" command). One of the following three formats may be used: ? The full path name that starts with '/' (e.g. /dev/sda). ? The device name only. This will prefix the directory name given by the -d option (e.g. sda). ? The major and minor number of the device separated by ':'. This will create a temporary device node in the device direc- tory (e.g. 8:0). The temporary name will be "tmpdev-<major>:<minor>-<pid>". RETURN VALUE The mpath_prio_alua command returns the following values: 0 on success. In this case the priority for the device is printed to stdout. The priority value is: 50 for devices that are in the active, optimized group 10 for devices that are in an active but non-optimized group 1 for devices that are in the standby group 0 for all other groups The reason for the widely spaced priority values is the way mul- tipath handles them. It will multiply the number of paths in a group with the priority value and select the group with the highest result. Thus, if there are six paths in the active, non- optimized group and only one in the active, optimized one, the non-optimized group would be used. 1 Indicates an error parsing the command line. 2 The given devices could not be opened for reading. 3 The device does not support target port groups. 4 The inquiry command did not return a target port group for the given device. 5 The report target port group command failed or did not return a target port group that was obtained from the inquiry command. EXAMPLES This example queries a device directly and returns the priority string: #> mpath_prio_alua /dev/sda 50 Now the major and minor number is used to specify the device and ver- bose output is selected: #> mpath_prio_alua -v 8:0 Target port groups are implicitly supported. Reported target port group is 0 [active/optimized] 50 The following example shows the entries in the devices section of the multipath-tool configuration file (/etc/multipath.conf) to support an IBM DS6000 storage system: device { vendor "IBM " product "1750500 " path_grouping_policy group_by_prio prio_callout "/sbin/mpath_prio_alua -d/tmp %d" features "1 queue_if_no_path" path_checker tur } Notes: ? Depending on your default configuration not all keywords are required (e.g. if your path_checker is set to tur you don't have to use the path_checker statement in the device section). ? The entries for vendor and product must be strings that are 8 charac- ters long (for vendor) and 16 characters long (for product). The strings have to be padded with blanks if necessary. ? If you are working with hotpluggable devices whose device nodes are created by udev you should use the %d flag in the prio_callout state- ment. This is because a short time elapses between the devices being available and udev creating the device nodes. ? If under certain circumstances your storage subsystem temporarily reports failures on all paths, you should use the features statement showed in the example. This will configure the multipath volume to requeue I/O until a path becomes available again, instead of report- ing failures in that case. SEE ALSO multipath(8), AUTHORS mpath_prio_alua was developed by Jan Kunigk and adapted by Stefan Bader <shbader@de.ibm.com> multipath-tools July 2006 MPATH_PRIO_ALUA(8)