How to configure DM-Multipath from an iSCSI initiator to an iSCSI target in CentOS / RHEL

The procedure to configure DM-Multipath from an iSCSI initiator to an iSCSI target is presented, which assumes the following:

• The iSCSI target package is installed on the server.
• Targets and LUNs are configured on the iSCSI server.
• The iSCSI initiator package is installed on the client.
• The DM-Multipath package is installed on the client.
• The targets have been discovered by the client.
• An iSCSI session is active between the target and the initiator.
• The initiator has redundant network connections to the target.

Before enabling DM-Multipath on the client, there is no /etc/multipath.conf configuration file:

# ls /etc/multipath.conf

You can manually create this file or enable DM-Multipath with the mpathconf utility:

# mpathconf --enable

This command copies multipath.conf from the /usr/share/doc/device-mapper-multipath-[version] directory to the /etc directory.

Run the following command to enable DM-Multipath. Notice that the configuration file now exists:

# mpathconf --enable
# ls /etc/multipath.conf /etc/multipath.conf

Before starting the multipathd daemon, there are no mpathN devices in /dev/mapper:

# ls /dev/mapper/mpatha
ls: cannot access /dev/mapper/mpatha: No such file or directory

After starting the multipathd daemon, the mpathN device is created in /dev/mapper: # systemctl start multipathd

# ls /dev/mapper/mpatha
/dev/mapper/mpatha

Use the /dev/mapper/mpatha name when creating a partition, when creating an LVM physical volume, and when making and mounting a file system. If one of the network interfaces fails on the initiator, I/O continues through the remaining active interface.