admin-guide/device-mapper/dm-service-time.rst

2 dm-service-time
5 dm-service-time is a path selector module for device-mapper targets,
6 which selects a path with the shortest estimated service time for
10 of in-flight I/Os on a path with the performance value of the path.
11 The performance value is a relative throughput value among all paths
12 in a path-group, and it can be specified as a table argument.
14 The path selector name is 'service-time'.
26 			among all paths in the path-group.
27 			The valid range is 0-100.
30 			other paths having a positive value are available.
34     <status> <fail-count> <in-flight-size> <relative_throughput>
36 		'A' if the path is active, 'F' if the path is failed.
37 	<fail-count>:
39 	<in-flight-size>:
40 		The size of in-flight I/Os on the path.
43 		among all paths in the path-group.
49 dm-service-time adds the I/O size to 'in-flight-size' when the I/O is
51 Basically, dm-service-time selects a path having minimum service time
54 	('in-flight-size' + 'size-of-incoming-io') / 'relative_throughput'
60 	   the division and just compare the 'in-flight-size'.
62 	2. If the paths have the same 'in-flight-size', skip the division
65 	3. If some paths have non-zero 'relative_throughput' and others
82   # echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4" \
86   test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 1 8:16 128 4
89   test: 0 10 multipath 2 0 0 0 1 1 E 0 2 2 8:0 A 0 0 1 8:16 A 0 0 4
92 Or '2' for sda and '8' for sdb would be also true::
94   # echo "0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8" \
98   test: 0 10 multipath 0 0 1 1 service-time 0 2 2 8:0 128 2 8:16 128 8
101   test: 0 10 multipath 2 0 0 0 1 1 E 0 2 2 8:0 A 0 0 2 8:16 A 0 0 8