Red Hat ENTERPRISE LINUX 5 - DM MULTIPATH, Руководство по настройке и администрированию

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Chapter 4. The DM-Multipath Configuration File
20
Attribute Description
prio_callout
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.
path_checker
Specifies the default method used to determine the state of
the paths. Possible values include
readsector0
and
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”
.
hardware_handler
Specifies a module that will be used to perform hardware specific
actions when switching path groups or handling I/O errors.
Possible values include
0
,
1 emc
, and
1 rdac
. The default value
is
0
.
rr_weight
If set to
priorities
, then instead of sending
rr_min_io
requests to a path before calling
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_callout
program. Currently, there are priority callouts only
for devices that use the
group_by_prio
path grouping policy,
which means that all the paths in a path group will always have the
same priority.
If set to
uniform
, all path weights are equal. The default value is
uniform
.
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 queuing.
A value of
queue
indicates that queuing should not stop until the
path is fixed.
The default value is (null).
failback
Specifies path group failback.
A value of 0 or
immediate
specifies that as soon as there is a
path group with 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.
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. The default
value is 1000.