Filter
Top Products
152 Administering dynamic multipathing (DMP)
Administering DMP using vxdmpadm
# dd if=/dev/vx/rdsk/mydg/myvol1 of=/dev/null &
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 Round-Robin 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 Round-Robin 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