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 the sample output from the vxdisk list command, the device has eight primary paths:
# vxdisk list sdq Device: sdq . . . numpaths: 8 sdj state=enabled type=primary sdk state=enabled type=primary sdl state=enabled type=primary sdm state=enabled type=primary sdn state=enabled type=primary sdo state=enabled type=primary sdp state=enabled type=primary sdq 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 &
Use the vxdmpadm iostat command to display the DMP statistics for the device. The sample output shows that all I/O is being directed to one path.
# vxdmpadm iostat show dmpnodename=sdq interval=5 count=2 . . . cpu usage = 11294us per cpu memory = 32768b OPERATIONS KBYTES AVG TIME(ms) PATHNAME READS WRITES READS WRITES READS WRITES sdj 0 0 0 0 0.00 0.00 sdk 0 0 0 0 0.00 0.00 sdl 0 0 0 0 0.00 0.00 sdm 0 0 0 0 0.00 0.00 sdn 0 0 0 0 0.00 0.00 sdo 0 0 0 0 0.00 0.00 sdp 0 0 0 0 0.00 0.00 sdq 10986 0 5493 0 0.41 0.00
Use the vxdmpadm getattr command 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
The above output 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, set the policy 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
Reset the DMP statistics:
# vxdmpadm iostat reset
With the workload still running, you can see the effect of changing the I/O policy to balance the load across the primary paths.
# vxdmpadm iostat show dmpnodename=sdq interval=5 count=2 . . . cpu usage = 14403us per cpu memory = 32768b OPERATIONS KBYTES AVG TIME(ms) PATHNAME READS WRITES READS WRITES READS WRITES sdj 2041 0 1021 0 0.39 0.00 sdk 1894 0 947 0 0.39 0.00 sdl 2008 0 1004 0 0.39 0.00 sdm 2054 0 1027 0 0.40 0.00 sdn 2171 0 1086 0 0.39 0.00 sdo 2095 0 1048 0 0.39 0.00 sdp 2073 0 1036 0 0.39 0.00 sdq 2042 0 1021 0 0.39 0.00
Enter the following command to return the enclosure to the single active I/O policy.
# vxdmpadm setattr enclosure ENC0 iopolicy=singleactive