Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 3, Administering Dynamic Multipathing (DMP)
Administering DMP Using vxdmpadm
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By running the vxdmpadm iostat command to display the DMP statistics for the device,
it can be seen that all I/O is being directed to one path, c5t4d15:
# vxdmpadm iostat show dmpnodename=c3t2d15 interval=5 count=2
...
cpu usage = 11294us per cpu memory = 32768b
OPERATIONS KBYTES AVG TIME(ms)
PATHNAME READS WRITES READS WRITES READS WRITES
c2t0d15 0 0 0 0 0.000000 0.000000
c2t1d15 0 0 0 0 0.000000 0.000000
c3t1d15 0 0 0 0 0.000000 0.000000
c3t2d15 0 0 0 0 0.000000 0.000000
c4t2d15 0 0 0 0 0.000000 0.000000
c4t3d15 0 0 0 0 0.000000 0.000000
c5t3d15 0 0 0 0 0.000000 0.000000
c5t4d15 5493 0 5493 0 0.411069 0.000000
The vxdmpadm command is used to display the I/O policy for the enclosure that contains
the device:
# vxdmpadm getattr enclosure ENC0 iopolicy
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