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How to use Linux Multipath on our storage together with other vendors

Publication Date:  2013-03-20 Views:  71 Downloads:  0
Issue Description
This can be used for all SAN product.Such as T serials and Dorado.
Alarm Information
If we don't do this, there will no load banlance.
Handling Process
1. Add Huawei device in /etc/multipath.conf 
If you can't find multipath.conf, you can copy one from /usr/share/doc/device-mapper-multipath-0.4.9/  to /etc。

Add device{} below devices.The detail is as below.
devices {
#       device {
#       }

        #
        # Huawei Dorado2100 : load banlance
        #
        device {
                vendor                  "HUAWEI"        # depond on the truth
                product                 "Dorado2100"      # depond on the truth
                path_grouping_policy    multibus
                getuid_callout          "/lib/udev/scsi_id --whitelisted --device=/dev/%n"
                path_checker            tur
                path_selector           "round-robin 0"
                rr_weight               priorities
                rr_min_io_rq            10  #default value, can be modified.
                failback                immediate
        }
}

2.Restart multipath service to let it work.The command is:
service multipathd restart
Root Cause
The description of the parameter in Multipath:

Attribute
Description

wwid
Specifies the WWID of the multipath device to which the multipath attributes apply. This parameter is mandatory for this section of the multipath.conf file.

alias
Specifies the symbolic name for the multipath device to which the multipath attributes apply. If you are using user_friendly_names, do not set this value to mpathn; this may conflict with an automatically assigned user friendly name and give you incorrect device node names.

path_grouping_policy
Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include:

failover = 1 path per priority group

multibus = all valid paths in 1 priority group

group_by_serial = 1 priority group per detected serial number

group_by_prio = 1 priority group per path priority value

group_by_node_name = 1 priority group per target node name


path_selector
Specifies the default algorithm to use in determining what path to use for the next I/O operation. Possible values include:

round-robin 0: Loop through every path in the path group, sending the same amount of I/O to each.

queue-length 0: Send the next bunch of I/O down the path with the least number of outstanding I/O requests.

service-time 0: Send the next bunch of I/O down the path with the shortest estimated service time, which is determined by dividing the total size of the outstanding I/O to each path by its relative throughput.


failback
Manages path group failback.

A value of immediate specifies immediate failback to the highest priority path group that contains active paths.

A value of manual specifies that there should not be immediate failback but that failback can happen only with operator intervention.

A value of followover specifies that automatic failback should be performed when the first path of a path group becomes active. This keeps a node from automatically failing back when another node requested the failover.

A numeric value greater than zero specifies deferred failback, expressed in seconds.


prio
Specifies the default function to call to obtain a path priority value. For example, the ALUA bits in SPC-3 provide an exploitable prio value. Possible values include:

const: Set a priority of 1 to all paths.

emc: Generate the path priority for EMC arrays.

alua: Generate the path priority based on the SCSI-3 ALUA settings.

tpg_pref: Generate the path priority based on the SCSI-3 ALUA settings, using the preferred port bit.

ontap: Generate the path priority for NetApp arrays.

rdac: Generate the path priority for LSI/Engenio RDAC controller.

hp_sw: Generate the path priority for Compaq/HP controller in active/standby mode.

hds: Generate the path priority for Hitachi HDS Modular storage arrays.


no_path_retry
A numeric value for this attribute specifies the number of times the system should attempt to use a failed path before disabling queueing.

A value of fail indicates immediate failure, without queueing.

A value of queue indicates that queueing should not stop until the path is fixed.


rr_min_io
Specifies the number of I/O requests to route to a path before switching to the next path in the current path group. This setting is only for systems running kernels older that 2.6.31. Newer systems should use rr_min_io_rq. The default value is 1000.

rr_min_io_rq
Specifies the number of I/O requests to route to a path before switching to the next path in the current path group, using request-based device-mapper-multipath. This setting should be used on systems running current kernels. On systems running kernels older than 2.6.31, use rr_min_io. The default value is 1.

rr_weight
If set to priorities, then instead of sending rr_min_io requests to a path before calling path_selector to choose the next path, the number of requests to send is determined by rr_min_io times the path's priority, as determined by the prio function. If set to uniform, all path weights are equal.

flush_on_last_del
If set to yes, then multipath will disable queueing when the last path to a device has been deleted.

END