mpath_prio_alua(8)

1MPATH_PRIO_ALUA(8)       Linux Administrator's Manual       MPATH_PRIO_ALUA(8)
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NAME

6       mpath_prio_alua - Path priority tool based on Asymmetric LUn Access
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SYNOPSIS

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

12       mpath_prio_alua  is  used  as a priority callout for the multipath com‐
13       mand. It returns a number that is used by multipath  to  group  devices
14       with the same priority together.
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OPTIONS

17       -d directory
18              target  directory  for devices given as relative device names or
19              devices given as major:minor number.  Default is "/dev".
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21       -h     displays the command line help.
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23       -v     turns on verbose output. This shows all results in  human  read‐
24              able format.  This includes information about the port group the
25              device is in and its current state.
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27       -V     shows the version number and exits.
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29       device specifies the device to query (the device must be a SCSI  device
30              that  supports the “Report Target Port Groups” command).  One of
31              the following three formats may be used:
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33              · The full path name that starts with '/' (e.g. /dev/sda).
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35              · The device name only. This  will  prefix  the  directory  name
36                given by the -d option (e.g. sda).
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38              · The  major  and  minor  number of the device separated by ':'.
39                This will create a temporary device node in the device  direc‐
40                tory    (e.g.    8:0).    The    temporary    name   will   be
41                “tmpdev-<major>:<minor>-<pid>”.
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RETURN VALUE

44       The mpath_prio_alua command returns the following values:
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46       0      on success. In this case the priority for the device is  printed
47              to stdout. The priority value is:
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49              50     for devices that are in the active, optimized group
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51              10     for devices that are in an active but non-optimized group
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53              1      for devices that are in the standby group
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55              0      for all other groups
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57              The reason for the widely spaced priority values is the way mul‐
58              tipath handles them. It will multiply the number of paths  in  a
59              group  with  the  priority  value  and select the group with the
60              highest result. Thus, if there are six paths in the active, non-
61              optimized  group  and only one in the active, optimized one, the
62              non-optimized group would be used.
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64       1      Indicates an error parsing the command line.
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66       2      The given devices could not be opened for reading.
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68       3      The device does not support target port groups.
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70       4      The inquiry command did not return a target port group  for  the
71              given device.
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73       5      The  report target port group command failed or did not return a
74              target port group that was obtained from the inquiry command.
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EXAMPLES

77       This example queries a device directly and returns the priority string:
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79              #> mpath_prio_alua /dev/sda
80              50
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82       Now the major and minor number is used to specify the device  and  ver‐
83       bose output is selected:
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85              #> mpath_prio_alua -v 8:0
86              Target port groups are implicitly supported.
87              Reported target port group is 0 [active/optimized]
88              50
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90       The  following  example shows the entries in the devices section of the
91       multipath-tool configuration file (/etc/multipath.conf) to  support  an
92       IBM DS6000 storage system:
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94              device {
95                     vendor                "IBM       "
96                     product               "1750500         "
97                     path_grouping_policy  group_by_prio
98                     prio_callout          "/sbin/mpath_prio_alua -d/tmp %d"
99                     features              "1 queue_if_no_path"
100                     path_checker          tur
101              }
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103       Notes:
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105       · Depending on your default configuration not all keywords are required
106         (e.g. if your path_checker is set to tur you don't have  to  use  the
107         path_checker statement in the device section).
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109       · The entries for vendor and product must be strings that are 8 charac‐
110         ters long (for vendor) and 16 characters  long  (for  product).   The
111         strings have to be padded with blanks if necessary.
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113       · If  you  are working with hotpluggable devices whose device nodes are
114         created by udev you should use the %d flag in the prio_callout state‐
115         ment.  This is because a short time elapses between the devices being
116         available and udev creating the device nodes.
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118       · If under certain circumstances  your  storage  subsystem  temporarily
119         reports  failures on all paths, you should use the features statement
120         showed in the example.  This will configure the multipath  volume  to
121         requeue  I/O until a path becomes available again, instead of report‐
122         ing failures in that case.
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AUTHORS

128       mpath_prio_alua was developed by Jan Kunigk and adapted by Stefan Bader
129       <shbader@de.ibm.com>
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133multipath-tools                    July 2006                MPATH_PRIO_ALUA(8)