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Creating Multiple Paths to a LUN

This topic applies to Logger Appliances only.

The HBA card on your Logger has two ports. You can connect both of those ports to the same LUN. Using those ports to create two different paths between the Logger and the LUN (multipathing) reduces the possibility of a single point of failure causing the LUN to become unavailable. 

Logger provides a default multipath configuration as a starting point. However, make sure that you consult your SAN documentation for information specific to your environment.

You must connect the LUN to both HBA ports and configure multipath configuration in the UI for it to function. Once enabled, multipath cannot be disabled on Logger.

You do not need to enable multipath in order to connect to two different LUNs on different SANs, since there are no duplicate paths. To connect to two different LUNs on the same SAN, or to have two connections to the same LUN, you must configure multipathing. Otherwise, the OS will see duplicate paths to the same LUN, and will be unable to resolve which path to use.

To enable multipath for a new Logger installation, configure multipathing before attaching the LUN.

To enable multipath:

  1. Ensure that a LUN is not attached to the Logger.
  2. Click System Admin from the top-level menu bar.
  3. Click Multipath in the Storage section in the left panel.
  4. Select a SAN multipathing configuration from the pull-down menu.
  5. If you chose Custom, or if the displayed configuration does not meet your needs, customize the parameters.

  6. Click Test to ensure that the configuration you chose or the changes you made are valid.

    If the test fails, make additional changes, or click Reset to start over.

  7. Click Save.

When you configure multipath SAN connectivity to the appliance, you must also make sure that the multipathd service is configured to start on boot.

To verify that the multipathd service is configured to start on boot:

  1. Run chkconfig --list multipathd

    Make sure '#:on' is shown for your run level. The current run level can be displayed with the 'runlevel' command.

  2. If the service is not enabled, do so with:
    chkconfig multipathd on

  3. Reboot the appliance or start the multipath daemon with:
    /sbin/service multipathd start

    Note: Be sure to also configure any vendor-specific multipath configuration accordingly in the /etc/multipath.conf file.

To convert a single path LUN to multipath:

  1. Connect to your Logger using SSH, as described in SSH Access to the Appliance.

  2. Run these commands:

    cd /opt/arcsight/aps/mpath
    ./mpath_prepare.sh
  3. Connect the second fiber cable to the second port on the HBA card.

  4. Run this test command:

    ./mpath_test.sh <path_to_your_multipath.conf >

    Review the output of the test command to ensure that multipath devices that will be created are listed at the bottom of the output.

  5. If the test output is not correct, repeat the steps and Run this test command: until the multipath devices are correctly listed.

  6. Run this command:

    ./mpath_enable.sh <path_to_your_multipath.conf >
  7. Reboot your appliance.