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 shown 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, use the dd command to apply an input workload from the volume:
# 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 0.00 0.00 c2t1d15 0 0 0 0 0.00 0.00 c3t1d15 0 0 0 0 0.00 0.00 c3t2d15 0 0 0 0 0.00 0.00 c4t2d15 0 0 0 0 0.00 0.00 c4t3d15 0 0 0 0 0.00 0.00 c5t3d15 0 0 0 0 0.00 0.00 c5t4d15 5493 0 5493 0 0.41 0.00
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 MinimumQ 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 MinimumQ 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 0.39 0.00 c2t1d15 947 0 947 0 0.39 0.00 c3t1d15 1004 0 1004 0 0.39 0.00 c3t2d15 1027 0 1027 0 0.40 0.00 c4t2d15 1086 0 1086 0 0.39 0.00 c4t3d15 1048 0 1048 0 0.39 0.00 c5t3d14 1036 0 1036 0 0.39 0.00 c5t4d15 1021 0 1021 0 0.39 0.00
The enclosure can be returned to the single active I/O policy by entering the following command:
# vxdmpadm setattr enclosure ENC0 iopolicy=singleactive