User guide

© DataDirect Networks 2011. Multipath (V1.8) User Guide | 21
10.3 VARIOUS
10.3.1 DEFAULT FOR PG_PRIO_CALC HAS CHANGED BETWEEN MULTIPATH VERSION 0.4.8
AND 0.4.9
Description:
The default for pg_prio_calc method has changed from “sum” in 0.4.8 to “avg” in 0.4.9.
With 0.4.8 (pg_prio_calc = “sum”) the priority of the path group is set to the sum of all path
weights in the group. Thus in the priority group below the priority is 600, which is the sum of
the six available paths which each have an individual path priority of 100.
# multipath -ll
360001ff080329000000002df8af00004 dm-8 SGI,DD6A-IS16K-10000
[size=1.0T][features=1 queue_if_no_path][hwhandler=0][rw]
\_ round-robin 0 [prio=600][enabled]
\_ 3:0:8:4 sdcg 69:64 [active][ready]
\_ 3:0:12:4 sddu 71:192 [active][ready]
\_ 3:0:14:4 sdeo 129:0 [active][ready]
\_ 4:0:8:4 sdik 135:64 [active][ready]
\_ 4:0:12:4 sdjy 65:448 [active][ready]
\_ 4:0:14:4 sdks 67:256 [active][ready]
With 0.4.9 (pg_prio_calc = “avg”) the priority is set to the average of the available paths in the
path group. Thus in the example below the priority is set to 100 for the priority group, which is
the average of the six available paths which each have an individual path priority of 100.
# multipath -ll
360001ff080329000000002df8af00004 dm-8 SGI,DD6A-IS16K-10000
[size=1.0T][features=1 queue_if_no_path][hwhandler=0][rw]
\_ round-robin 0 [prio=100][enabled]
\_ 3:0:8:4 sdcg 69:64 [active][ready]
\_ 3:0:12:4 sddu 71:192 [active][ready]
\_ 3:0:14:4 sdeo 129:0 [active][ready]
\_ 4:0:8:4 sdik 135:64 [active][ready]
\_ 4:0:12:4 sdjy 65:448 [active][ready]
\_ 4:0:14:4 sdks 67:256 [active][ready]
Workaround:
Edit the /etc/multipath.conf file to add the pg_prio_calc option. The addition must be made to
the “default” section of the multipath.conf file, not in a device section.
Example:
defaults {
udev_dir /dev
user_friendly_names no
pg_prio_calc avg
}
Warning: This setting may impact the default behavior of other vendor storage devices.