VERITAS Volume Manager 4.1 Administrator's Guide

Administering Dynamic Multipathing (DMP)
Administering DMP Using vxdmpadm
Chapter 3 145
ENCLR_NAME DEFAULT CURRENT
============================================
ENC0 Single-Active Single-Active
This shows that the policy for the enclosure is set to singleactive, which explains why all
the I/O is taking place on one path.
To balance the I/O load across the multiple primary paths, the policy is set to round-robin as
shown here:
# vxdmpadm setattr enclosure ENC0 iopolicy=round-robin
# vxdmpadm getattr enclosure ENC0 iopolicy
ENCLR_NAME DEFAULT CURRENT
============================================
ENC0 Single-Active Round-Robin
The DMP statistics are now reset:
# vxdmpadm iostat reset
With the workload still running, the effect of changing the I/O policy to balance the load
across the primary paths can now be seen.
# vxdmpadm iostat show dmpnodename=c3t2d15 interval=5 count=2
...
cpu usage = 14403us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t0d15 1021 0 1021 0 0.396670 0.000000
c2t1d15 947 0 947 0 0.391763 0.000000
c3t1d15 1004 0 1004 0 0.393426 0.000000
c3t2d15 1027 0 1027 0 0.402142 0.000000
c4t2d15 1086 0 1086 0 0.390424 0.000000
c4t3d15 1048 0 1048 0 0.391221 0.000000
c5t3d15 1036 0 1036 0 0.390927 0.000000
c5t4d15 1021 0 1021 0 0.392752 0.000000
The enclosure can be returned to the single active I/O policy by entering the following
command:
# vxdmpadm setattr enclosure ENC0 iopolicy=singleactive