1=============== 2dm-queue-length 3=============== 4 5dm-queue-length is a path selector module for device-mapper targets, 6which selects a path with the least number of in-flight I/Os. 7The path selector name is 'queue-length'. 8 9Table parameters for each path: [<repeat_count>] 10 11:: 12 13 <repeat_count>: The number of I/Os to dispatch using the selected 14 path before switching to the next path. 15 If not given, internal default is used. To check 16 the default value, see the activated table. 17 18Status for each path: <status> <fail-count> <in-flight> 19 20:: 21 22 <status>: 'A' if the path is active, 'F' if the path is failed. 23 <fail-count>: The number of path failures. 24 <in-flight>: The number of in-flight I/Os on the path. 25 26 27Algorithm 28========= 29 30dm-queue-length increments/decrements 'in-flight' when an I/O is 31dispatched/completed respectively. 32dm-queue-length selects a path with the minimum 'in-flight'. 33 34 35Examples 36======== 37In case that 2 paths (sda and sdb) are used with repeat_count == 128. 38 39:: 40 41 # echo "0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128" \ 42 dmsetup create test 43 # 44 # dmsetup table 45 test: 0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128 46 # 47 # dmsetup status 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 49