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-rw-r--r-- | Documentation/device-mapper/dm-queue-length.txt | 39 |
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diff --git a/Documentation/device-mapper/dm-queue-length.txt b/Documentation/device-mapper/dm-queue-length.txt new file mode 100644 index 000000000000..f4db2562175c --- /dev/null +++ b/Documentation/device-mapper/dm-queue-length.txt | |||
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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 | ||