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151Administering dynamic multipathing (DMP)
Administering DMP using vxdmpadm
# vxdmpadm setattr arrayname DISK iopolicy=singleactive
Scheduling I/O on the paths of an Asymmetric Active/Active
array
You can specify the use_all_paths attribute in conjunction with the adaptive,
balanced, minimumq, priority and round-robin I/O policies to specify whether
I/O requests are to be scheduled on the secondary paths in addition to the
primary paths of an Asymmetric Active/Active (A/A-A) array. Depending on the
characteristics of the array, the consequent improved load balancing can
increase the total I/O throughput. However, this feature should only be enabled
if recommended by the array vendor. It has no effect for array types other than
A/A-A.
For example, the following command sets the balanced I/O policy with a
partition size of 2048 blocks (2MB) on the enclosure enc0, and allows
scheduling of I/O requests on the secondary paths:
# vxdmpadm setattr enclosure enc0 iopolicy=balanced \
partitionsize=2048 use_all_paths=no
The default setting for this attribute is use_all_paths=no.
Example of applying load balancing in a SAN
This example describes how to configure load balancing in a SAN environment
where there are multiple primary paths to an Active/Passive device through
several SAN switches. As can be seen in this sample output from the
vxdisk
list command, the device c3t2d15 has eight primary paths:
# vxdisk list c3t2d15
Device: c3t2d15
...
numpaths: 8
c2t0d15 state=enabled type=primary
c2t1d15 state=enabled type=primary
c3t1d15 state=enabled type=primary
c3t2d15 state=enabled type=primary
c4t2d15 state=enabled type=primary
c4t3d15 state=enabled type=primary
c5t3d15 state=enabled type=primary
c5t4d15 state=enabled type=primary
In addition, the device is in the enclosure ENC0, belongs to the disk group mydg,
and contains a simple concatenated volume myvol1.
The first step is to enable the gathering of DMP statistics:
# vxdmpadm iostat start
Next the dd command is used to apply an input workload from the volume: