1*f0ba4377SMauro Carvalho Chehab=============== 2fd5e0339SKiyoshi Uedadm-queue-length 3fd5e0339SKiyoshi Ueda=============== 4fd5e0339SKiyoshi Ueda 5fd5e0339SKiyoshi Uedadm-queue-length is a path selector module for device-mapper targets, 6fd5e0339SKiyoshi Uedawhich selects a path with the least number of in-flight I/Os. 7fd5e0339SKiyoshi UedaThe path selector name is 'queue-length'. 8fd5e0339SKiyoshi Ueda 9fd5e0339SKiyoshi UedaTable parameters for each path: [<repeat_count>] 10*f0ba4377SMauro Carvalho Chehab 11*f0ba4377SMauro Carvalho Chehab:: 12*f0ba4377SMauro Carvalho Chehab 13fd5e0339SKiyoshi Ueda <repeat_count>: The number of I/Os to dispatch using the selected 14fd5e0339SKiyoshi Ueda path before switching to the next path. 15fd5e0339SKiyoshi Ueda If not given, internal default is used. To check 16fd5e0339SKiyoshi Ueda the default value, see the activated table. 17fd5e0339SKiyoshi Ueda 18fd5e0339SKiyoshi UedaStatus for each path: <status> <fail-count> <in-flight> 19*f0ba4377SMauro Carvalho Chehab 20*f0ba4377SMauro Carvalho Chehab:: 21*f0ba4377SMauro Carvalho Chehab 22fd5e0339SKiyoshi Ueda <status>: 'A' if the path is active, 'F' if the path is failed. 23fd5e0339SKiyoshi Ueda <fail-count>: The number of path failures. 24fd5e0339SKiyoshi Ueda <in-flight>: The number of in-flight I/Os on the path. 25fd5e0339SKiyoshi Ueda 26fd5e0339SKiyoshi Ueda 27fd5e0339SKiyoshi UedaAlgorithm 28fd5e0339SKiyoshi Ueda========= 29fd5e0339SKiyoshi Ueda 30fd5e0339SKiyoshi Uedadm-queue-length increments/decrements 'in-flight' when an I/O is 31fd5e0339SKiyoshi Uedadispatched/completed respectively. 32fd5e0339SKiyoshi Uedadm-queue-length selects a path with the minimum 'in-flight'. 33fd5e0339SKiyoshi Ueda 34fd5e0339SKiyoshi Ueda 35fd5e0339SKiyoshi UedaExamples 36fd5e0339SKiyoshi Ueda======== 37fd5e0339SKiyoshi UedaIn case that 2 paths (sda and sdb) are used with repeat_count == 128. 38fd5e0339SKiyoshi Ueda 39*f0ba4377SMauro Carvalho Chehab:: 40*f0ba4377SMauro Carvalho Chehab 41fd5e0339SKiyoshi Ueda # echo "0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128" \ 42fd5e0339SKiyoshi Ueda dmsetup create test 43fd5e0339SKiyoshi Ueda # 44fd5e0339SKiyoshi Ueda # dmsetup table 45fd5e0339SKiyoshi Ueda test: 0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128 46fd5e0339SKiyoshi Ueda # 47fd5e0339SKiyoshi Ueda # dmsetup status 48fd5e0339SKiyoshi Ueda 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