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4.4. 멀티패스 장치 설정 속성

표 4.2. “멀티패스 속성 ” shows the attributes that you can set in the multipaths section of the multipath.conf configuration file for each specific multipath device. These attributes apply only to the one specified multipath. These defaults are used by DM Multipath and override attributes set in the defaults and devices sections of the multipath.conf file.

표 4.2. 멀티패스 속성

속성 설명
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
미지정된 멀티패스에 적용할 기본값 경로 그룹 정책을 지정합니다. 가능한 값은 다음과 같습니다:
failover = 우선 순위 그룹 당 1 개의 경로
multibus = 1 개의 우선 순위 그룹에 있는 유효한 모든 경로
group_by_serial = 검색된 시리얼 번호 당 1 개의 우선 순위 그룹
group_by_prio = 경로 우선 순위 값 당 1 개의 우선 순위 그룹
group_by_node_name = 대상 노드 이름 당 1 개의 우선 순위 그룹
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.
0 보다 큰 숫자 값을 지정하여 초 단위로 지연 장애 복구가 되도록 합니다.
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. As of Red Hat Enterprise Linux 7.3, if you specify prio "alua exclusive_pref_bit" in your device configuration, multipath will create a path group that contains only the path with the pref bit set and will give that path group the highest priority.
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.
features
The default extra features of multipath devices, using the format: "number_of_features_plus_arguments feature1 ...".
Possible values for features include:
queue_if_no_path, which is the same as setting no_path_retry to queue. For information on issues that may arise when using this feature, see 5.6절. “Issues with queue_if_no_path feature”.
retain_attached_hw_handler: If this parameter is set to yes and the SCSI layer has already attached a hardware handler to the path device, multipath will not force the device to use the hardware_handler specified by the multipath.conf file. If the SCSI layer has not attached a hardware handler, multipath will continue to use its configured hardware handler as usual. The default value is no.
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.
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 queuing.
fail 값은 대기 상태 없이 즉시 장애가 발생함을 나타냅니다.
queue 값은 경로가 수정될 때 까지 대기 상태가 계속 됨을 나타냅니다.
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 queuing when the last path to a device has been deleted.
user_friendly_names If set to yes, specifies that the system should use the /etc/multipath/bindings file to assign a persistent and unique alias to the multipath, in the form of mpathn. If set to no, specifies that the system should use use the WWID as the alias for the multipath. In either case, what is specified here will be overridden by any device-specific aliases you specify in the multipaths section of the configuration file.
delay_watch_checks (Red Hat Enterprise Linux Release 7.2 and later) If set to a value greater than 0, the multipathd daemon will watch paths that have recently become valid for the specified number of checks. If they fail again while they are being watched, when they next become valid they will not be used until they have stayed up for the number of consecutive checks specified with delay_wait_checks. This allows you to keep paths that may be unreliable from immediately being put back into use as soon as they come back online.
delay_wait_checks (Red Hat Enterprise Linux Release 7.2 and later) If set to a value greater than 0, when a device that has recently come back online fails again within the number of checks specified with delay_watch_checks, the next time it comes back online it will be marked and delayed and it will not be used until it has passed the number of checks specified in delay_wait_checks.
deferred_remove If set to yes, multipathd will do a deferred remove instead of a regular remove when the last path device has been deleted. This ensures that if a multipathed device is in use when a regular remove is performed and the remove fails, the device will automatically be removed when the last user closes the device.
skip_kpartx (Red Hat Enterprise Linux Release 7.3 and later) If set to yes, kpartx will not automatically create partitions on the device. This allows users to create a multipath device without creating partitions, even if the device has a partition table.
max_sectors_kb (Red Hat Enterprise Linux Release 7.4 and later) Sets the max_sectors_kb device queue parameter to the specified value on all underlying paths of a multipath device before the multipath device is first activated. When a multipath device is created, the device inherits the max_sectors_kb value from the path devices. Manually raising this value for the multipath device or lowering this value for the path devices can cause multipath to create I/O operations larger than the path devices allow. Using the max_sectors_kb parameter is an easy way to set these values before a multipath device is created on top of the path devices and prevent invalid-sized I/O operations from being passed If this parameter is not set by the user, the path devices have it set by their device driver, and the multipath device inherits it from the path devices.
reservation_key
This is the service action reservation key used by mpathpersist. It must be set for all multipath devices using persistent reservations, and it 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. If the --param-aptpl option is used when registering the key with mpathpersist, :aptpl must be appended to the end of the reservation key.
As of Red Hat Enterprise Linux Release 7.5, this parameter can be set to file, which will store the RESERVATION KEY registered by mpath‐persist in the prkeys_file file. The multipathd daemon will then use this key to register additional paths as they appear. When the registration is removed, the RESERVATION KEY is removed from the prkeys_file file.
다음 예에서는 두 개의 특정한 멀티패스 장치에 해당하는 설정 파일에 지정된 멀티패스 속성을 보여주고 있습니다. 첫 번째 장치는 WWID 3600508b4000156d70001200000b0000과 yellow라는 상징적 이름을 가지고 있습니다.
예에서 두 번째 멀티패스 장치는 WWID 1DEC_____321816758474와 red라는 상징적 이름을 가지고 있습니다. 예에서, rr_weight 속성은 priorities로 설정되어 있습니다. 
multipaths {
       multipath {
              wwid                  3600508b4000156d70001200000b0000
              alias                 yellow
              path_grouping_policy  multibus
              path_selector         "round-robin 0"
              failback              manual
              rr_weight             priorities
              no_path_retry         5
       }
       multipath {
              wwid                  1DEC_____321816758474
              alias                 red
              rr_weight             priorities
        }
}