Red Hat CLUSTER SUITE 4.7 DM MULTIPATH Configuration And Administration Manual page 28

Chapter 4. The DM-Multipath Configuration File
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 IO/ 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.
Attribute
vendor
product
bl_product
path_grouping_policy
getuid_callout
prio_callout
path_checker
path_selector
failback
features
18
Description
Specifies the vendor name of the storage device to which the
device attributes apply, for example COMPAQ.
Specifies the product name of the storage device to which the
device attributes apply, for example HSV110 (C)COMPAQ.
Specifies a regular expression used to blacklist devices by vendor/
product. Note that for a device to get blacklisted, the vendor,
product, and bl_product strings must all match.
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
Specifies the default program and arguments to call out to obtain a
unique path identifier. An absolute path is required.
Specifies the 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 failue. "none" is a
valid value.
Specifies the default method used to determine the state of
the paths. Possible values include readsector0 and tur,
emc_clariion, hp_sw, and directio.
Specifies the default algorithm to use in determining what path to
use for the next I/O operation.
Specifies path group failback.
A value of 0 or immediate specifies that as soon as there is a
path group whith a higher priority than the current path group the
system switches to that path group.
A numeric value greater than zero specifies deferred failback,
expressed in seconds.
A value of manual specifies that failback can happen only with
operator intervention.
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.