Multipath configuration for FC-NVMe hosts

Follow FC-NVMe multipath configuration recommendations for successful attachment of Linux hosts to the system.

On SLES15, complete the following steps to disable native multipath:
1. Create a kernel module configuration file.
```
echo "options nvme_core multipath=N" > /etc/modprobe.d/50-nvme_core.conf
```
2. Rebuild RAMDISK.
```
dracut -f
```
3. Restart the host.
Based on operating system support, further updates are expected.
Ensure that the Emulex auto-connect mechanism is installed, such as by entering rpm -ivh nvmefc-connect-12.0.261.15-1.sles15sp0.x86_64.rpm.

Linux multipath setting.

devices {
    device {
        vendor "NVME"
        product "IBM     2145"
        path_grouping_policy "multibus"
        path_selector "round-robin 0"
        prio "const"
        path_checker "none"
        failback "immediate"
        no_path_retry "queue"
        rr_weight uniform
        rr_min_io_rq "1"
        fast_io_fail_tmo 15
        dev_loss_tmo 600
    }
}
defaults {
    user_friendly_names yes
    path_grouping_policy    group_by_prio
}

Multiqueue I/O scheduling with blk-mq (in SLES). Edit the /etc/default/grub file and add dm_mod.use_blk_mq=y to the current settings of the GRUB_CMDLINE_LINUX_DEFAULT variable.

GRUB_CMDLINE_LINUX_DEFAULT="BOOTPTimeout=20 BootpWait=20 biosdevname=0 powersaved=off
 resume=/dev/system/swap splash=silent quiet showopts crashkernel=175M,high dm_mod.use_blk_mq=y"

Apply the new configuration.

swfc178:~ # grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found theme: /boot/grub2/themes/SLE/theme.txt
Found linux image: /boot/vmlinuz-4.12.14-25.19-default
Found initrd image: /boot/initrd-4.12.14-25.19-default
Found linux image: /boot/vmlinuz-4.12.14-23-default
Found initrd image: /boot/initrd-4.12.14-23-default
done

Restart the system.  Validate that the multiqueue function is enabled in multipath.

mpathj (eui.88000000000000000050760071b78044) dm-3 NVME,IBM     2145
size=12G features='2 queue_mode mq' hwhandler='0' wp=rw