Download Red Hat Enterprise Linux 7 Logical Volume Manager Administration

T he Device Mapper
In the following example, the no _path_retry attribute in the mul ti path. co nf file has
been set to queue I/O operations only until all paths have been marked as failed after a set
number of attempts have been made to use the paths. In this case, the mapping appears as
follows until all the path checkers have failed the specified number of checks.
0 71014400 multipath 1 queue_if_no_path 0 2 1 round-robin 0 2 1
66:128 \
1000 65:64 1000 round-robin 0 2 1 8:0 1000 67:192 1000
After all the path checkers have failed the specified number of checks, the mapping would
appear as follows.
0 71014400 multipath 0 0 2 1 round-robin 0 2 1 66:128 1000 65:64
1000 \
round-robin 0 2 1 8:0 1000 67:192 1000
#handlerargs
The number of hardware handler arguments, followed by those arguments. A hardware
handler specifies a module that will be used to perform hardware-specific actions when
switching path groups or handling I/O errors. If this is set to 0, then the next parameter is
#pathgroups.
#pathgroups
The number of path groups. A path group is the set of paths over which a multipathed
device will load balance. There is one set of pathgroupargs parameters for each path
group.
pathgroup
The next path group to try.
pathgroupsargs
Each path group consists of the following arguments:
pathselector #selectorargs #paths #pathargs device1 ioreqs1 ...
deviceN ioreqsN
There is one set of path arguments for each path in the path group.
pathselector
Specifies the algorithm in use to determine what path in this path group to use for
the next I/O operation.
#selectorargs
The number of path selector arguments which follow this argument in the
multipath mapping. Currently, the value of this argument is always 0.
#paths
The number of paths in this path group.
#pathargs
The number of path arguments specified for each path in this group. Currently this
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