1 =============== 1 ===============
2 dm-queue-length 2 dm-queue-length
3 =============== 3 ===============
4 4
5 dm-queue-length is a path selector module for 5 dm-queue-length is a path selector module for device-mapper targets,
6 which selects a path with the least number of 6 which selects a path with the least number of in-flight I/Os.
7 The path selector name is 'queue-length'. 7 The path selector name is 'queue-length'.
8 8
9 Table parameters for each path: [<repeat_count 9 Table parameters for each path: [<repeat_count>]
10 10
11 :: 11 ::
12 12
13 <repeat_count>: The number of I/Os to 13 <repeat_count>: The number of I/Os to dispatch using the selected
14 path before switching 14 path before switching to the next path.
15 If not given, internal 15 If not given, internal default is used. To check
16 the default value, see 16 the default value, see the activated table.
17 17
18 Status for each path: <status> <fail-count> <i 18 Status for each path: <status> <fail-count> <in-flight>
19 19
20 :: 20 ::
21 21
22 <status>: 'A' if the path is active, ' 22 <status>: 'A' if the path is active, 'F' if the path is failed.
23 <fail-count>: The number of path failu 23 <fail-count>: The number of path failures.
24 <in-flight>: The number of in-flight I 24 <in-flight>: The number of in-flight I/Os on the path.
25 25
26 26
27 Algorithm 27 Algorithm
28 ========= 28 =========
29 29
30 dm-queue-length increments/decrements 'in-flig 30 dm-queue-length increments/decrements 'in-flight' when an I/O is
31 dispatched/completed respectively. 31 dispatched/completed respectively.
32 dm-queue-length selects a path with the minimu 32 dm-queue-length selects a path with the minimum 'in-flight'.
33 33
34 34
35 Examples 35 Examples
36 ======== 36 ========
37 In case that 2 paths (sda and sdb) are used wi 37 In case that 2 paths (sda and sdb) are used with repeat_count == 128.
38 38
39 :: 39 ::
40 40
41 # echo "0 10 multipath 0 0 1 1 queue-length 41 # echo "0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128" \
42 dmsetup create test 42 dmsetup create test
43 # 43 #
44 # dmsetup table 44 # dmsetup table
45 test: 0 10 multipath 0 0 1 1 queue-length 0 45 test: 0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128
46 # 46 #
47 # dmsetup status 47 # dmsetup status
48 test: 0 10 multipath 2 0 0 0 1 1 E 0 2 1 8:0 48 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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