Ernst, a regular poster of the Dutch VMug, posted a script for load balancing paths to an active/active SAN. What it does is select the next path for a LUN, in other words if there are four paths LUN1 will be reached via Path1, LUN2 via Path2 etc.

The script, also available for download here:

#!/bin/bash
for PATHS in 2 4 6 8
do
STPATHS=${PATHS}
COUNTER=”1″

for LUN in $(esxcfg-mpath -l | grep “has ${STPATHS} paths” | awk ‘{print $2}’)
do
esxcfg-mpath –lun=${LUN} –path=$(esxcfg-mpath -q –lun=${LUN} | grep FC | awk ‘{print $4}’ | awk ‘{print NR “S\t ” $0}’ | grep ${COUNTER}S | awk ‘{print $2}’) –preferred
COUNT=`expr ${COUNTER} + 1`
COUNTER=${COUNT}
if [[ ${COUNTER} -gt ${STPATHS} ]]
then
COUNTER=”1″
fi
done
done

This will result in the following outcome with “esxcfg-mpath -l”:

Disk vmhba2:1:4 /dev/sdh (512000MB) has 4 paths and policy of Fixed
FC 16:0.1 50060b0000646c8a<->50060e8004f2e812 vmhba2:1:4 On active preferred
FC 16:0.1 50060b0000646c8a<->50060e8004f2e873 vmhba2:2:4 On
FC 19:0.1 50060b0000646062<->50060e8004f2e802 vmhba4:1:4 On
FC 19:0.1 50060b0000646062<->50060e8004f2e863 vmhba4:2:4 On

Disk vmhba2:1:5 /dev/sdi (512000MB) has 4 paths and policy of Fixed
FC 16:0.1 50060b0000646c8a<->50060e8004f2e812 vmhba2:1:5 On
FC 16:0.1 50060b0000646c8a<->50060e8004f2e873 vmhba2:2:5 On active preferred
FC 19:0.1 50060b0000646062<->50060e8004f2e802 vmhba4:1:5 On
FC 19:0.1 50060b0000646062<->50060e8004f2e863 vmhba4:2:5 On

Disk vmhba2:1:6 /dev/sdj (307200MB) has 4 paths and policy of Fixed
FC 16:0.1 50060b0000646c8a<->50060e8004f2e812 vmhba2:1:6 On
FC 16:0.1 50060b0000646c8a<->50060e8004f2e873 vmhba2:2:6 On
FC 19:0.1 50060b0000646062<->50060e8004f2e802 vmhba4:1:6 On active preferred
FC 19:0.1 50060b0000646062<->50060e8004f2e863 vmhba4:2:6 On

Disk vmhba2:1:7 /dev/sdk (307200MB) has 4 paths and policy of Fixed
FC 16:0.1 50060b0000646c8a<->50060e8004f2e812 vmhba2:1:7 On
FC 16:0.1 50060b0000646c8a<->50060e8004f2e873 vmhba2:2:7 On
FC 19:0.1 50060b0000646062<->50060e8004f2e802 vmhba4:1:7 On
FC 19:0.1 50060b0000646062<->50060e8004f2e863 vmhba4:2:7 On active preferred

Disk vmhba2:1:8 /dev/sdl (512000MB) has 4 paths and policy of Fixed
FC 16:0.1 50060b0000646c8a<->50060e8004f2e812 vmhba2:1:8 On active preferred
FC 16:0.1 50060b0000646c8a<->50060e8004f2e873 vmhba2:2:8 On
FC 19:0.1 50060b0000646062<->50060e8004f2e802 vmhba4:1:8 On
FC 19:0.1 50060b0000646062<->50060e8004f2e863 vmhba4:2:8 On

Disk vmhba2:1:9 /dev/sdm (512000MB) has 4 paths and policy of Fixed
FC 16:0.1 50060b0000646c8a<->50060e8004f2e812 vmhba2:1:9 On
FC 16:0.1 50060b0000646c8a<->50060e8004f2e873 vmhba2:2:9 On active preferred
FC 19:0.1 50060b0000646062<->50060e8004f2e802 vmhba4:1:9 On
FC 19:0.1 50060b0000646062<->50060e8004f2e863 vmhba4:2:9 On

In other words, when you run this script each LUN will be addressed via a specific path and all HBA’s and SAN Disk Controllers will be used instead of the default first path / first controller policy. This will result in a better performance and distribution of load on the SAN Disk Controllers.