The multipath utility is the device mapper target auto-configurator, which is used to detect and configure multiple paths to devices. Use the following command to display usage:
# multipath -h
multipath-tools v0.4.9 (05/33, 2016)
Usage:
multipath [-a|-A|-c|-w|-W] [-d] [-T tm:val] [-r] [-i] [-v lvl] [-p pol] [-b fil] [-q] [dev]
multipath -l|-ll|-f [-v lvl] [-b fil] [dev]
multipath -F [-v lvl]
multipath -t
multipath -h
Where:
-h print this usage text
-l show multipath topology (sysfs and DM info)
-ll show multipath topology (maximum info)
-f flush a multipath device map
-F flush all multipath device maps
-a add a device wwid to the wwids file
-A add devices from kernel command line mpath.wwids
parameters to wwids file
-c check if a device should be a path in a multipath device
-T tm:val
check if tm matches the multipathd timestamp. If so val is
whether or not the device is a path in a multipath device
-q allow queue_if_no_path when multipathd is not running
-d dry run, do not create or update devmaps
-t dump internal hardware table
-r force devmap reload
-i ignore wwids file
-B treat the bindings file as read only
-b fil bindings file location
-w remove a device from the wwids file
-W reset the wwids file include only the current devices
-p pol force all maps to specified path grouping policy :
. failover one path per priority group
. multibus all paths in one priority group
. group_by_serial one priority group per serial
. group_by_prio one priority group per priority lvl
. group_by_node_name one priority group per target node
-v lvl verbosity level
. 0 no output
. 1 print created devmap names only
. 2 default verbosity
. 3 print debug information
dev action limited to:
. multipath named 'dev' (ex: mpath0) or
. multipath whose wwid is 'dev' (ex: 60051..)
. multipath including the path named 'dev' (ex: /dev/sda)
. multipath including the path with maj:min 'dev' (ex: 8:0)
Some of the available options are described as follows:
- -v [verbosity] – Specify the verbosity level when displaying paths and multipaths.
- -l – List the multipath topology.
- -ll – List the maximum multipath topology information.
- -f – Flush a multipath device map. Use –F to flush all multipath device maps.
- -c – Check if a device should be a path in a multipath device.
- -p failover | multibus | group_by_serial | group_by_prio |group_by_node_name – Force all maps to the specified path grouping policy.
- -r – Force device map reload.
You can optionally specify a device name to update only the device map that contains the specified device. Use the /dev/sd# format, the major:minor format, the multipath map name (for example, mpathN), or the WWID to specify a device.
A sample output of the multipath –ll command is as follows:
# multipath -ll
...
mpathb(36001405346939038cc9480caf0dd9a9d) dm-3 LIO-ORG ,IBLOCK size=10g features=‘0’ hwhandler=‘0’ wp=rw
‘-+- policy=‘service-time 0’ prio=1 status=active
‘- 2:0:0:2 sdb 8:16 active ready running
mpatha(36001405a7c28190541f4d61880050090) dm-2 LIO-ORG ,IBLOCK size=10g features=‘0’ hwhandler=‘0’ wp=rw
‘-+- policy=‘service-time 0’ prio=1 status=active
‘- 2:0:0:1 sda 8:0 active ready running
...
The output for mpathb is described as follows:
- mpathb – User-friendly device name
- 36001405346939038cc9480caf0dd9a9d – Unique WWID
- dm-3 – sysfs file name
- LIO-ORG – Vendor name
- IBLOCK – Linux BLOCK device
- size=10g – Size of the DM device
- features=‘0’ – DM features supported
- hwhandler=‘0’ – Hardware handler
- wp=rw – Write permission, set to read-write
- policy=‘service-time 0’ – Path selector algorithm
- prio=1 – Path group priority
- status=active – Path group state
- 2:0:0:2 – SCSI information: host, channel, scsi_id, and LUN
- sdb – Linux device name
- 8:16 – Major and minor numbers
- active ready running – DM path and physical path state