The current LUN configurations for RHEL5 hosts is setup for active-passive
configurations and uses the “1 emc” hardware handler.
 
To take advantage of ALUA [Asymmetric Logical Unit Access] mode (active active)
The multipath config file should be used .

# This is an example configuration file for device mapper multipath.
# For a complete list of the default configuration values, see
# /usr/share/doc/device-mapper-multipath-0.4.5/multipath.conf.defaults
# For a list of configuration options with descriptions, see
# /usr/share/doc/device-mapper-multipath-0.4.5/multipath.conf.annotated 
# Blacklist all devices by default. Remove this to enable multipathing
# on the default devices.
#devnode_blacklist {
# devnode "*"
#}
## Use user friendly names, instead of using WWIDs as names.
#defaults {
# user_friendly_names yes
#}
##
## This is a template multipath-tools configuration file
## Uncomment the lines relevent to your environment
##
defaults {
#            udev_dir /dev
#            polling_interval 10
#            selector "round-robin 0"
#            path_grouping_policy multibus
#            getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
#            prio_callout /bin/true
#            path_checker tur#             rr_min_io 100#            rr_weight priorities#            failback immediate#            no_path_retry queueuser_friendly_names yes}
##
## The wwid line in the following blacklist section is shown as an example
## of how to blacklist devices by wwid. The 3 devnode lines are the
## compiled in default blacklist.
##
#devnode_blacklist {
blacklist {
#            wwid 26353900f02796769
              devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
              devnode "^hd[a-z]"
              devnode "^cciss!c[0-9]d[0-9]*
              devnode "sda"
}
devices {
             device {
                         vendor "DGC"
                         product "*"
                         path_grouping_policy group_by_prio
                         getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
                         prio_callout "/sbin/mpath_prio_alua /dev/%n"
                         path_checker directio
                         path_selector "round-robin 0"
                         features "1 queue_if_no_path"
                         no_path_retry 300
                         hardware_handler "1 alua"
                         failback immediate
              }
}