49 lines
1.2 KiB
ReStructuredText
49 lines
1.2 KiB
ReStructuredText
|
===============
|
||
|
|
dm-queue-length
|
||
|
|
===============
|
||
|
|
|
||
|
|
dm-queue-length is a path selector module for device-mapper targets,
|
||
|
|
which selects a path with the least number of in-flight I/Os.
|
||
|
|
The path selector name is 'queue-length'.
|
||
|
|
|
||
|
|
Table parameters for each path: [<repeat_count>]
|
||
|
|
|
||
|
|
::
|
||
|
|
|
||
|
|
<repeat_count>: The number of I/Os to dispatch using the selected
|
||
|
|
path before switching to the next path.
|
||
|
|
If not given, internal default is used. To check
|
||
|
|
the default value, see the activated table.
|
||
|
|
|
||
|
|
Status for each path: <status> <fail-count> <in-flight>
|
||
|
|
|
||
|
|
::
|
||
|
|
|
||
|
|
<status>: 'A' if the path is active, 'F' if the path is failed.
|
||
|
|
<fail-count>: The number of path failures.
|
||
|
|
<in-flight>: The number of in-flight I/Os on the path.
|
||
|
|
|
||
|
|
|
||
|
|
Algorithm
|
||
|
|
=========
|
||
|
|
|
||
|
|
dm-queue-length increments/decrements 'in-flight' when an I/O is
|
||
|
|
dispatched/completed respectively.
|
||
|
|
dm-queue-length selects a path with the minimum 'in-flight'.
|
||
|
|
|
||
|
|
|
||
|
|
Examples
|
||
|
|
========
|
||
|
|
In case that 2 paths (sda and sdb) are used with repeat_count == 128.
|
||
|
|
|
||
|
|
::
|
||
|
|
|
||
|
|
# echo "0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128" \
|
||
|
|
dmsetup create test
|
||
|
|
#
|
||
|
|
# dmsetup table
|
||
|
|
test: 0 10 multipath 0 0 1 1 queue-length 0 2 1 8:0 128 8:16 128
|
||
|
|
#
|
||
|
|
# dmsetup status
|
||
|
|
test: 0 10 multipath 2 0 0 0 1 1 E 0 2 1 8:0 A 0 0 8:16 A 0 0
|