HP Veritas Volume Manager 5.0 -UX 11i v3 manual 151

152Administering 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-robinas 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