Sunday, 11 May 2014

The Linux multipath Command

This is a very dangerous command. Document everything and backup everything when you use it.

Use the Linux multipath(8) command to configure and manage multipathed devices.
General syntax for the multipath(8) command:

multipath [-v verbosity] [-d] [-h|-l|-ll|-f|-F] [-p failover|multibus|group_by_serial|group_by_prio|group_by_node_name] 

General Examples

Configure multipath devices:


Configure a specific multipath device:

multipath devicename

Replace devicename

 Replace devicename with the device node name such as /dev/sdb (as shown by udev in the $DEVNAME variable), or in the major:minor format.Selectively suppress a multipath map, and its device-mapped partitions:
multipath -f

Display potential multipath devices

Display potential multipath devices, but do not create any devices and do not update device maps (dry run):
multipath -d

Configure multipath devices and display multipath map information:

multipath -v2  
multipath -v3
The -v2 option in multipath -v2 -d shows only local disks. Use the -v3 option to show the full path list.lliiFor example:
multipath -v3 -d

Display the status of all multipath devices, or a specified multipath device:

multipath -ll 
multipath -ll 

Flush all unused multipath device maps 

Flush all unused multipath device maps (unresolves the multiple paths; it does not delete the device):
multipath -F
multipath -F  

Set the group policy:

multipath -p [failover|multibus|group_by_serial|group_by_prio|group_by_node_name] 
Group Policy Options for the multipath -p Command
Policy Option Description
failover One path per priority group. You can use only one path at a time.
multibus All paths in one priority group.
group_by_serial One priority group per detected SCSI serial number (the controller node worldwide number).
group_by_prio One priority group per path priority value. Paths with the same priority are in the same priority group. Priorities are determined by callout programs specified as a global, per-controller, or per-multipath option in the /etc/multipath.conf configuration file.
group_by_node_name One priority group per target node name. Target node names are fetched in the /sys/class/fc_transport/target*/node_name location.

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