k3s/pkg/volume/README.md

Multipath

To leverage multiple paths for block storage, it is important to perform the multipath configuration on the host. If your distribution does not provide /etc/multipath.conf, then you can either use the following minimalistic one:

defaults {
    find_multipaths yes
    user_friendly_names yes
}

or create a new one by running:

$ mpathconf --enable

Finally you'll need to ensure to start or reload and enable multipath:

$ systemctl enable multipathd.service
$ systemctl restart multipathd.service

Note: Any change to multipath.conf or enabling multipath can lead to inaccessible block devices, because they'll be claimed by multipath and exposed as a device in /dev/mapper/*.

Some additional informations about multipath can be found in the iSCSI documentation