Multipath configuration for FC-NVMe hosts

Turning Native NVMe Multipath on or off

• On SLES15, Native NVMe Multipath is turned on by default. On SLES12SP4, Native NVMe Multipath is not turned on by default.
  To check whether Native NVMe Multipath is on, enter:

  # systool -m nvme_core -A multipath
  Module = "nvme_core"
  
      multipath           = "Y"

  If the multipath = "N", and you want to turn it on, enter:

  
  echo "options nvme_core multipath=Y" > /etc/modprobe.d/50-nvme_core.conf
  dracut -f
  reboot

  Note: On SLES12SP4, if the multipath is not turned on even after reboot, then follow these steps:

  1. Edit the file /etc/default/grub.
  2. Append nvme-core.multipath=on at the end of the GRUB_CMDLINE_LINUX_DEFAULT variable.
  3. Save the file.
  4. Run grub2-mkconfig -o /boot/grub2/grub.cfg to apply the new configuration.
  5. Reboot.
  If you choose to work with Device Mapper, enter:

  echo "options nvme_core multipath=N" > /etc/modprobe.d/50-nvme_core.conf
  dracut -f
  reboot

• On Red Hat Enterprise Linux 8.0 or later, Native NVMe Multipath is not turned on by default.
  To check whether Native NVMe Multipath is enabled in the command-line, enter:

  # cat /sys/module/nvme_core/parameters/multipath
  
      Y

  If the output is "N", and you want to enable it, follow these steps:

  • Using command-line:
    1. Add the nvme_core.multipath=Y option on the command-line:

       # grubby --update-kernel=ALL --args="nvme_core.multipath=Y"

    2. On the 64-bit IBM Z architecture, update the boot menu:

       # zipl
       

    3. Reboot the system.
  • Using module configuration file:
    1. Create the /etc/modprobe.d/nvme_core.conf configuration file with the following content:

       options nvme_core multipath=Y

    2. Back up the initramfs file system:

       # cp /boot/initramfs-$(uname -r).img \
            /boot/initramfs-$(uname -r).bak.$(date +%m-%d-%H%M%S).img

    3. Rebuild the initramfs file system:

       # dracut --force --verbose

    4. Reboot the system.
  If you choose to work with Device Mapper, enter:

  1. Remove the nvme_core.multipath=Y option from the command-line:

     # grubby --update-kernel=ALL --remove-args="nvme_core.multipath=Y"

  2. On the 64-bit IBM Z architecture, update the boot menu:

     # zipl

  3. Remove the options nvme_core multipath=Y line from the /etc/modprobe.d/nvme_core.conf file, if it is present.
  4. Reboot the system.

  For more details to enable native NVMe and Device Mapper on Red Hat Enterprise Linux 8.0 or later, see https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_device_mapper_multipath/enabling-multipathing-on-nvme-devices_configuring-device-mapper-multipath#doc-wrapper.

Device Mapper or Native NVMe Multipath configuration

Two framework options are available to configure the multipath configuration file: Device Mapper or Native NVMe Multipath.

blacklist {
    device {
        vendor  "NVME"
        product "IBM\s+2145"
    }
}

Device Mapper performance