devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
 devnode "^hd[a-z]"

blacklist_exceptions {
        # by wwid
        wwid  36000d310000065000000000000000030
        wwid  36000d310000065000000000000000031
}

defaults {
        ## if yes, use /etc/multipath/bindings to assign mpathn names
       ## if no, use wwid for multipath (default)
       ##
       ## wwid device names: /dev/disk/by-id/scsi-xxxxxxxx
       ##
       ## user-friendly device names: /dev/mapper/mpathN
       ##
       ##     unique and persistent through /etc/multipath/bidnings or /var/lib/multipath/bidnings
       ##     that stores and tracks wwn <-> N mapping
       ##
       ##     can be problematic for file systems containing root and /etc, or /var;
       ##     in the latter case can modify bindings file location with bindings_file
       ##
       ## alias names: /dev/mapper/<alias>
       ##
       ##     can be problematic for file systems containing root and /etc
       ##
       ## in cluster use wwid names or alias names, since user-friendly names are
       ## node-local and not cluster-global (unless bindings file is manually
       ## replicated)
       ##
        # user_friendly_names no
        # bindings_file "/etc/multipath/bindings"

        # if yes, create multipaths only if there are 2+ paths to the same wwid
        # if no, create multipaths to all non-blacklisted devices
        find_multipaths yes

        ## directory where udev creates its device nodes
        # udev_dir /dev

        ## directory for plugins
        # multipath_dir "/lib/multipath"

        ## verbosity level (0 to 6, default = 2)
        # verbosity 2

        ## interval between two path checks (seconds, default: 5)
        # polling_interval 5

        ## specify the timeout for path checkers, to detect the path has failed,
        ## this is a timeout for SCSI command
        ## default is taken from /sys/block/sdx/device/timeout
        # checker_timeout 30 # in seconds

        ## FibreChannel specific timeout values
        # fast_io_fail_tmo ...
        # dev_loss_tmo ...

        ## method to determine the path's state
        # path_checker readsector0   # read the first sector of the device (default)
        # path_checker directio      # read the first sector with direct I/O
        # path_checker tur           # issue SCSI command TEST UNIT READY to the device,
                                     # preferred compared to readsector or directio if the LUN supports tur,
                                     # as on failure it does not fill up the system log with messages
                                     #
                                     #    to verify TUR works fine, can issue manually:
                                     #        sg_turs -v /dev/sdx
                                     #
        # path_checker emc_clarion   # query EMC Clarion specific EVPD page 0xC0 to determine path state
        # path_checker hp_sw         # query HP storage array firmware
        # path_checker rdac          # RDAC LSI/Engenio storage controller proprietory


        ## If set to "once" , multipathd logs the first path checker error at logging level 2,
        ## any later errors are logged at level 3 until the device is restored.
        ## If set to "always" , multipathd always logs the path checker error at logging level 2.
        ## Default is "always".
        # log_checker_err "always"

        ## path selector algorithm to use within a primary ptjgroup
        # path_selector "round-robin 0"      # spread load equally among all paths in the pathgroup
        # path_selector "queue-length 0"     # send next request batch to the path with the least amount of outstanding IO
        # path_selector "service-time 0"     # choose path for the next request batch based on the amount of outstanding IO
                                             # to the path and its relative throughput

        ## path grouping policy:
        ##
        ##     multibus            - all paths in the same priority group, traffic is load-balanced across
        ##                           all active paths in the group
        ##     failover            - separate priority group per each path, so only one path is used at a time
        ##     group_by_serial     - separate priority group per detected serial number (WWID)
        ##     group_by_node_name  - separate priority group per target node name (sys/class/fc_transport/target*/node_name)
        ##     group_by_prio       - separate priority group per each priority value; priorities are determined by
        ##                           callout program specified in the config file on a per-multipath, per-controller
        ##                           or global basis (parameter prio_callout)
        ##        
        ## A priority group is a set of paths that go to the same physical LUN.
        ## By default, I/O is distributed in a round-robin fashion across all paths in the group,
        ## unless alternatove path_selector is specified.
        ## The multipath framework multiplies the number of paths in a group by the group’s priority to determine
        ## which group is the primary. The group with the highest calculated value is the primary.
        ## When all paths in the primary group are failed, the priority group with the next highest value becomes active.       
        ##        
        # path_grouping_policy "multibus"

        ## Callout program and args used to obtain path priority values,
        ## when path_grouping_policy is "group_by_prio".
        ##
        ## Implemented for EMC, NetApp, Compaq/HP, Hitachi and other vendors, as well as for SCSI-3 ALUA.
        ##
        ## The specified program will be executed and should return a numeric value specifying
        ## the relative priority of this path. Higher number have a higher priority.
        ## A ’%n’ in the command line will be expanded to the device name, a ’%b’ will be expanded
        ## to the device number in major:minor format.
        ##
        ## Default is "none".
        ##
        # prio_callout none
        # prio_callout mpath_prio_alua /dev/%n

        ## default program and args to obtain a unique path identifier
        # getuid_callout "/lib/udev/scsi_id -g -u -s"
        # getuid_callout "/lib/udev/scsi_id --replace-whitespace --whitelisted --device=/dev/%n"

        ## device-mapper features to be used
        ## format is "number_of_features_plus_arguments feature1 ..."
        # features "1 queue_if_no_path"
       ## "queue_if_no_path" is equaivalent to setting no_path_retry to "queue" - i.e. if all paths
       ## are broke, all processes waiting for IO will hang until one or more paths are restored
       ##
       ## to disable queuing, set features to "0" and set no_path_retry to let us say 50
       ## see more in here
       ##
       ## pg_init_retries <n>      Retry path group initialization up to n times before failing
       ##                          where 1 <= n <= 50
       ##
       ## pg_init_delay_msecs <n>  Wait n milliseconds between path group initialization retries
       ##                          where 0 <= n <= 60000
       ##
       # features "4 pg_init_delay_msecs 1000 pg_init_retries 30"

        ## number of times to retry the path until multipath fails the path and disables queueing to it
        ##
        # no_path_retry 5      # retry specified number of times
        # no_path_retry 0      # (default) fail over right away
        # no_path_retry fail   # immediate failure (no queueing), same as "0"
        # no_path_retry queue  # never stop queueing - keep queueing forever until the path comes alive

        ## only for kernels < 2.6.31, newer ones use rr_min_io_rq
        ## number of IO's to route to a paths before switching to next path in the same group (default: 1000)
        # rr_min_io 1000

        ## number of IO's to route to a paths before switching to next path in the same group (default: 1)
        # rr_min_io_rq 1
       
        ## if set to "priorities", configurator will assign path weights as "path prio * rr_min_io_rq"
        ## if set to "uniform", all path weights are equal
        # rr_weight "priorities"
        # rr_weight "uniform"

        ## If set to "yes", multipath will try to detect if the device supports ALUA.
        ## If so, the device will automatically use the ALUA prioritizer.
        ## If not, the prioritizer will be selected as usual.
        ## Default is "no".
        ##         
        # detect_prio "no"

        ## default method to set priority to the paths
        ##         
        # prio const        # set priority 1 to all paths (default)
        # prio alua         # generate path priority based on SCSI-3 ALUA settings
        # prio tpr_pref     # generate path priority based on SCSI-3 ALUA settings, using the preferred port bit
        # prio emc          # for EMC arrays
        # prio ontap        # for NetApp arrays
        # prio rdac         # for LSI/Engenio/NetApp E-series RDAC controller
        # prio hp_sw        # for HP/Compaq controller in active/standby mode
        # prio hds          # for Hitachi arrays

        ## Specifies whether to monitor the failed path recovery, and indicates the timing for group failback
        ## after failed paths return to service.
        ## When the failed path recovers, the path is added back into the multipath-enabled path list based on
        ## this setting. Multipath evaluates the priority groups, and changes the active priority group when
        ## the priority of the primary path exceeds the secondary group.
        ##         
        # failback immediate    # When a path recovers, enable the path immediately.
        # failback 5            # When the path recovers, wait n seconds before enabling the path.
                                # Specify an integer value greater than 0.
        # failback manual       # (Default) The failed path is not monitored for recovery.
                                # The administrator runs the multipath command to update enabled paths and priority groups.
        # failback followover   # only perform automatic failback when the first path of a pathgroup becomes active,
                                # this keeps a node from automatically failing back when another node requested
                                # the failover

        ## if set to "no", multipathd will disable queueing for all devices when it is shut down (default: "yes")
        # queue_without_daemon "yes"

        ## if set to "yes", multipathd will disable queueing for all devices when the last path
        ## to the device has been deleted (default: "no")
        # flush_on_last_del "yes"

        ## Service action reservation key used by mpathpersist.
        ## Must be set for all multipath devices using persistent reservations.
        ## Must be the same as the RESERVATION KEY field of the PERSISTENT RESERVE OUT parameter list
        ## which contains an 8-byte value provided by the application client to the device server
        ## to identify the I_T nexus.
        ## Default: unset.
        ##
        # reservation_key ...

        ## udev attribute that provides a unique path identifier (default: ID_SERIAL)
        # uid_attribute "ID_SERIAL"
}

Can override here

path_grouping_policy
path_selector
failback
prio
prio_args
no_path_retry
rr_min_io
rr_weight
flush_on_last_del

multipaths {
        multipath {
                wwid                  3600508b4000156d700012000000b0000
               
                # alias: optional, symbolic name for multipath map
                alias                 data_1

                path_grouping_policy  multibus
                path_checker          readsector0
                path_selector         "round-robin 0"
                failback              manual
                rr_weight             priorities
                no_path_retry         5
        }
        multipath {
                wwid                  1DEC_____321816758474
                alias                 data_2
                rr_weight             priorities
        }
}

Can override here:

blacklist {
        wwid "*"
}

blacklist_exceptions {
        wwid 36e843b668f682e2d00a0d4740d912ada
}

defaults {
        # verbosity 2
        # bindings_file "/etc/multipath/bindings"
        user_friendly_names  no
        find_multipaths yes
        polling_interval 5
        rr_min_io_rq 1
        # getuid_callout "/lib/udev/scsi_id --replace-whitespace --whitelisted --device=/dev/%n"
        # queue_without_daemon yes
        # flush_on_last_del "yes"
}

devices {
        device {
                vendor "QNAP +"
                product "iSCSI Storage +"
                path_grouping_policy multibus
                path_selector "service-time 0"
                # path_checker readsector0   # read the first sector of the device (default)
                # path_checker directio      # read the first sector with direct I/O
                path_checker tur           # issue SCSI command TEST UNIT READY to the device
                failback 5
                prio const
                rr_weight uniform
                features "0"
                no_path_retry 0
        }
}

multipaths {
        multipath {
                wwid    36e843b668f682e2d00a0d4740d912ada
                alias   xs2
        }
}