Configure DM-Multipath

Contributors NetAppZacharyWambold

DM-Multipath manages multiple paths between the Linux host and the storage cluster. Configuring DM-Multipath on a LUN, which appears to the Linux host as a SCSI device, enables your Linux host to access its LUN on the storage cluster if a path or component fails.

Before you begin

You must have identified the required version of DM-Multipath from the Interoperability Matrix tool.

Note

The recommended approach is that you configure two paths per node into each fabric or Ethernet network. This allows a path to fail without the node switching over to its partner. Using link aggregation (LAG) for the physical ports is not recommended with a Windows-based operating system.

Steps
  1. Edit the /etc/multipath.conf file as follows:

    1. Determine whether there are non-NetApp SCSI devices to exclude (blacklist).

      These are devices that are not displayed when you enter the sanlun lun show command.

      • If there are non-NetApp SCSI devices to exclude, enter the worldwide identifier (WWID) for the devices in the blacklist section of the multipath.conf file.

      To display the WWID of a non-NetApp SCSI device, enter the following command on the device that you want to exclude, where SCSI_device_name is a device that you specify: /lib/udev/scsi_id -gud /dev/SCSI_device_name

      For example, if /dev/sda is the non-NetApp SCSI device that you want to exclude, you would enter the following: /lib/udev/scsi_id -gud /dev/sda

      This displays the WWID of the device, which you can copy and paste in the multipath.conf file.

      In the following example showing the blacklist section of the multipath.conf file, the non-NetApp SCSI device with WWID 3600508e000000000753250f933cc4606 is excluded:

      blacklist {
                  **wwid       3600508e000000000753250f933cc4606**
                  devnode    "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
                  devnode    "^hd[a-z]"
                  devnode     "^cciss.*"
      }
      • If there are no devices to exclude, remove the wwid line from the multipath.conf file.

    2. Enable NetApp recommended DM-Multipath settings by appending the following string to the end of the kernel line in the boot loader: rdloaddriver=scsi_dh_alua

  2. Start the DM-Multipath daemon: /etc/init.d/multipathd start

  3. Add the multipath service to the boot sequence so that the multipath daemon always starts during system boot: chkconfig multipathd on

  4. Reboot the Linux host.

  5. Verify that the rdloaddriver setting appears in the output when you run cat /proc/cmdline.

    The rdloaddriver setting appears as one of several boot options that are passed to the kernel:

    # cat /proc/cmdline
    ro root=/dev/mapper/vg_ibmx3650210104-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=vg_ibmx3650210104/lv_root SYSFONT=latarcyrheb-sun16 rd_LVM_LV=vg_ibmx3650210104/lv_swap crashkernel=129M@0M  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet **rdloaddriver=scsi_dh_alua**