How do I configure device-mapper-multipath for EMC CLARiion or VNX with ALUA mode in RHEL 6, 7?

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux 6, 7
  • device-mapper-multipath (DM-Multipath)
  • EMC Clariion/VNX/Unity storage array in Active-Active mode 4 (ALUA)

Issue

  • How do I configure multipath for EMC CLARiion or VNX for ALUA in RHEL 6?
  • I am using an EMC Clariion or VNX storage array and wish to configure multipath in active-active mode 4 (ALUA), what are the recommended configurations for active-active multipath?
  • Seeing "emc: ALUA failover mode detected" logged in messages

Resolution

Please see the information within the latest "EMC Host Connectivity Guide for Linux" available from EMC. It is highly recommended to consult EMC for proper configuration based on array class, firmware code, failover mode, etc. Failing to following EMC guidelines can result in the storage configuration being unsupported by EMC and undesired failover behavior during NDU.

  • Per latest Rev A47 P/N 300-003-865 of the Dell EMC Host Connectivity Guide for Linux dated December 2018, recommends the following clauses all Clariion/VNX/Unity class arrays that support ALUA:

    • RHEL 6.0 - 6.2 (see pg 197-198 within above vendor guide)

            devices {
        device {
          vendor "DGC"
          product ".*"
          product_blacklist "LUNZ"
          :
          path_checker emc_clariion   ### Rev 47 alua
          hardware_handler "1 alua"   ### modified for alua
          prio alua                   ### modified for alua
          :
        }
      }

    • RHEL 6.3 and later (see pg 198 within above vendor guide)

            devices {
        device {
          vendor "DGC"
          product ".*"
          product_blacklist "LUNZ"
          :
          path_checker emc_clariion   ### Rev 47 alua
          hardware_handler "1 alua"   ### modified for alua
          prio tpg_pref               ### modified for alua
          :
        }
      }

    • RHEL7.0 and later (see pg 199-200 within above vendor guide)

            devices {
        device {
          vendor "DGC"
          product ".*"
          product_blacklist "LUNZ"
          :
          path_checker emc_clariion   ### Rev 47 alua
          hardware_handler "1 alua"   ### modified for alua
          prio alua                   ### modified for alua
          :
        }
      }

    NOTE! The above only serves to highlight which fields within the device clause are to be modified for ALUA support. Do not simply cut & paste the above into multipath without the rest of the required fields.

  • Add and/or update the devices clause for DGC (CLARiiON) or VNX storage arrays within multipath.conf per above EMC document.

    • if a custom DGC clause already exists within multipath.conf file:
      • modify the three fields per above within the existing DGC device clause.
    • if no DGC clause is currently present within multipath.conf file:
      • place a copy of the default device clause for DGC (CLARiiON) or VNX storage arrays within multipath.conf
        • a copy of the default device clause is available from /usr/share/doc/device-mapper-multipath-0.4.9/multipath.conf.defaults
        • place the device { ... } clause between devices { ... } as show above to maintain proper multipath.conf syntax
      • remove the leading '#' comment character from the copied device clause
      • modify the three fields per above within the newly copied DGC device clause within multipath.conf

  • Reload the multipathd service for changes to take effect:

For RHEL 6:

    # service multipathd reload

For RHEL 7:

    # systemctl reload multipathd

Root Cause

  • The default path_checker is emc_clariion. As per EMC, emc_clariion path checker is optimized for Passive Not Ready (PNR) failover mode 1 and not for ALUA failover mode 4.
  • The hardware handler for PNR configurations is "emc", the hardware handler will output "emc: ALUA failover mode detected" when it detects ALUA mode capability within storage. This is a good indicator that the multipath.conf configuration is not correct for the storage configuration.
SBR
Product(s)
Components
Category
Tags

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.