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.

      1. 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**