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symbolic name of yellow.
The second multipath device in the example has a WWID of 1DEC_____321816758474 and a
symbolic name of red. In this example, the rr_weight attributes is set to priorities.
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
}
}
4.5. Configuration File Devices
Table 4.3, Device Attributes shows the attributes that you can set for each individual storage device in
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Red Hat Enterprise Linux 5 DM Multipath
the devices section of the multipath.conf configuration file. These attributes are used by DM-
Multipath unless they are overwritten by the attributes specified in the multipaths section of the
multipath.conf file for paths that contain the device. These attributes override the attributes set in
the defaults section of the multipath.conf file.
Many devices that support multipathing are included by default in a multipath configuration. The values
for the devices that are supported by default are listed in the multipath.conf.defaults file. You
probably will not need to modify the values for these devices, but if you do you can overwrite the default
values by including an entry in the configuration file for the device that overwrites those values. You can
copy the device configuration defaults from the multipath.conf.defaults file for the device and
override the values that you want to change.
To add a device to this section of the configuration file that is not configured automatically by default, you
need to set the vendor and product parameters. You can find these values by looking at
/sys/block/device_name/device/vendor and /sys/block/device_name/device/model
where device_name is the device to be multipathed, as in the following example:
# cat /sys/block/sda/device/vendor
WINSYS
# cat /sys/block/sda/device/model
SF2372
The additional parameters to specify depend on your specific device. If the device is active/active, you
will usually not need to set additional parameters. You may want to set path_grouping_policy to
multibus. Other parameters you may need to set are no_path_retry and rr_min_io, as
described in Table 4.3, Device Attributes .
If the device is active/passive, but it automatically switches paths with I/O to the passive path, you need
to change the checker function to one that does not send I/O to the path to test if it is working
(otherwise, your device will keep failing over). This almost always means that you set the
path_checker to tur; this works for all SCSI devices that support the Test Unit Ready command,
which most do.
If the device needs a special command to switch paths, then configuring this device for multipath
requires a hardware handler kernel module. The current hardware handlers are emc and rdac. If these
are not sufficient for your device, you may not be able to configure the device for multipath.
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Chapter 4. The DM-Multipath Configuration File
Table 4 .3. Device Attributes
Attribute Description
vendor Specifies the vendor name of the storage device to which the
device attributes apply, for example COMPAQ.
product Specifies the product name of the storage device to which the
device attributes apply, for example HSV110 (C)COMPAQ.
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
getuid_callout
Specifies the default program and arguments to call out to obtain a
unique path identifier. An absolute path is required.
This parameter accepts the following wildcard values:
%n: replaced with the device name as it appears in sysfs.
%c: replaced with the device name as it appears in /dev (this is
different than the sysfs name for CCISS devices). (Red Hat
Enterprise Linux 5.8 and later)
%d: replaced with major_nr:minor_nr
%h: replaced with host_nr:bus_nr:target_nr:lun_nr.
prio_callout Specifies the default program and arguments to call out to obtain a
path weight. Weights are summed for each path group to determine
the next path group to use in case of failure. "none" is a valid value.
This parameter accepts the same wildcard values as
getuid_callout.
path_checker Specifies the default method used to determine the state of the
paths. Possible values include readsector0, rdac, tur,
cciss_tur, hp_tur, emc_clariion, hp_sw, and directio.
path_selector Specifies the default algorithm to use in determining what path to
use for the next I/O operation.
features The extra features of multipath devices. The only existing feature is
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 Section 5.4, Issues with
queue_if_no_path feature .
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