Configuring device-mapper-multipath for an EMC DGC storage configured in ALUA mode with RHEL 5

Issue

• How to configure multipath for EMC CLARiiON and VNX for ALUA
• Multipath issues on EMC CLARiiON or VNX storage
• An EMC DGC storage device has been configured to use ALUA mode, and device-mapper-multipath on the host must be configured to use explicit ALUA mode
• My EMC DGC storage SAN paths are configured in active-active ALUA mode, what configuration do I need to apply to device-mapper-multipath?
• My EMC Clariion SAN paths are configured in active-active ALUA mode, what configuration do I need to apply to device-mapper-multipath?
• If I try to access paths (/dev/sdN) directly, the disks in the lower priority group will fail. Multipath device access still works OK when disabling the paths in the high priority group.
• Multipath displaying "kernel: Buffer I/O error on device sdX, logical block 0" with EMC CLARiiON SAN
• My system mounts LUNs on an EMC Clariion SAN. I see entries in /var/log/messages stating

kernel: Buffer I/O error on device sdX, logical block 0

• Storage LUNs automatically disappear when loaded.