Device Multipathing Sample Setup
You would typically configure multipathing on a system that can access storage on a Fibre Channel-based storage area network (SAN), or on an iSCSI initiator if redundant network connections exist between the initiator and the target.
Figure 9-1 shows a simple DM-Multipath configuration where two I/O paths are configured between a server and a disk on a SAN-attached storage array:
-
Between host bus adapter
hba1
on the server and controllerctrl1
on the storage array. -
Between host bus adapter
hba2
on the server and controllerctrl2
on the storage array.
Figure 9-1 DM-Multipath Mapping of Two Paths to a Disk over a SAN

Without DM-Multipath, the system treats each path as being
separate even though both paths connect to the same storage
device. DM-Multipath creates a single multipath device,
/dev/mapper/mpathN
,
that subsumes the underlying devices,
/dev/sdc
and /dev/sdf
.
The multipathing service (multipathd
) handles
I/O from and to a multipathed device in one of the following
ways:
- Active/Active
-
I/O is distributed across all available paths, either by round-robin assignment or dynamic load-balancing.
- Active/Passive (standby failover)
-
I/O uses only one path. If the active path fails, DM-Multipath switches I/O to a standby path. This is the default configuration.
Note:
DM-Multipath can provide failover in the case of path failure, such as in a SAN fabric. Disk media failure must be handled by using either a software or hardware RAID solution.
The naming of multipath devices is managed by multipathing's
user_friendly_names
property in the multipath.conf
file.
If set to no
, then the devices are named based on their World Wide
Identifiers (WWIDs) in /dev/mapper/WWID
. WWIDs are unique to their respective devices.
If the property is set to yes
, the devices
are mapped as
/dev/mapper/mpathN
,
where N is the multipath group
number. In addition, you can use the alias
attribute to assign meaningful names to the devices. See
Working With the Multipathing Configuration File.
To check the status of user_friendly_names
and other DM-multipath settings,
issue the mpathconf command, for example:
sudo mpathconf
Information similar to the following is displayed:
multipath is enabled find_multipaths is enabled user_friendly_names is enabled dm_multipath modules is loaded multipathd is running
Or, you can view the settings in /etc/multipath.conf
.
You can use the multipath device in
/dev/mapper
to reference the storage in the
same way as you would any other physical storage device. For
example, you can configure it as an LVM physical volume, file
system, swap partition, Automatic Storage Management (ASM) disk,
or raw device.