MAN page from Mandriva 2009 multipath-tools-0.4.8-4mdv2009.0.i586.rpm

MPATH_PRIO_ALUA

Section: \Linux Administrator's Manual (8)
Updated: July 2006
Index

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_aluais used as a priority callout for the multipath command. It returns a numberthat 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 givenasmajor: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 itscurrent state.

-V

shows the version number and exits.

device

specifies the device to query (the device must be a SCSI device that supportsthe lq]Report Target Port Groupsrq] 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 willcreate a temporary device node in the device directory (e.g. 8:0). Thetemporary name will belq]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 tostdout. 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 handlesthem. It will multiply the number of paths in a group with the priority valueand select the group with the highest result. Thus, if there are six paths inthe 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 targetport 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 verboseoutput 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 themultipath-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 touse the path_checker statement in the device section).
*: The entries for vendor and product must be strings that are 8characters 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 createdby udev you should use the %d flag in theprio_callout statement.This is because a short time elapses between the devices being availableand udev creating the device nodes.
*: If under certain circumstances your storage subsystem temporarily reportsfailures on all paths, you should use the features statement showedin the example.This will configure the multipath volume to requeue I/O until a path becomesavailable again, instead of reporting failures in that case.

AUTHORS

mpath_prio_aluawas developed by Jan Kunigk and adapted by Stefan Bader <shbaderAATTde.ibm.com>

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