Manual Reference Pages  - MPATH_PRIO_ALUA (8)

"Linux Administrator’s Manual"

NAME

mpath_prio_alua - Path priority tool based on Asymmetric LUn Access

CONTENTS

Synopsis
Description
Options
Authors

SYNOPSIS

mpath_prio_alua [-d directory] [-h] [-v] [-V] device [ device [ ... ]]

DESCRIPTION

mpath_prio_alua is used as a priority callout for the multipath command. 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 readable 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 lq]Report Target Port Groupsrq] command). One of the following three formats may be used:
o The full path name that starts with ’/’ (e.g. /dev/sda).
o The device name only. This will prefix the directory name given by the -d option (e.g. sda).
o The major and minor number of the device separated by ’:’. This will create a temporary device node in the device directory (e.g. 8:0). The temporary name will be lq]tmpdev-<major>:<minor>-<pid>rq].

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 multipath 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 verbose 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:
o 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).
o The entries for vendor and product must be strings that are 8 characters long (for vendor) and 16 characters long (for product). The strings have to be padded with blanks if necessary.
o If you are working with hotpluggable devices whose device nodes are created by udev you should use the %d flag in the prio_callout statement. This is because a short time elapses between the devices being available and udev creating the device nodes.
o 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 reporting 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 MPATH_PRIO_ALUA (8) July 2006
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