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Documentation / device-mapper / dm-queue-length.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:36 EST.

1	dm-queue-length
2	===============
3	
4	dm-queue-length is a path selector module for device-mapper targets,
5	which selects a path with the least number of in-flight I/Os.
6	The path selector name is 'queue-length'.
7	
8	Table parameters for each path: [<repeat_count>]
9		<repeat_count>: The number of I/Os to dispatch using the selected
10				path before switching to the next path.
11				If not given, internal default is used. To check
12				the default value, see the activated table.
13	
14	Status for each path: <status> <fail-count> <in-flight>
15		<status>: 'A' if the path is active, 'F' if the path is failed.
16		<fail-count>: The number of path failures.
17		<in-flight>: The number of in-flight I/Os on the path.
18	
19	
20	Algorithm
21	=========
22	
23	dm-queue-length increments/decrements 'in-flight' when an I/O is
24	dispatched/completed respectively.
25	dm-queue-length selects a path with the minimum 'in-flight'.
26	
27	
28	Examples
29	========
30	In case that 2 paths (sda and sdb) are used with repeat_count == 128.
31	
32	# echo "0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128" \
33	  dmsetup create test
34	#
35	# dmsetup table
36	test: 0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128
37	#
38	# dmsetup status
39	test: 0 10 multipath 2 0 0 0 1 1 E 0 2 1 8:0 A 0 0 8:16 A 0 0
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