Let's say you've acquired an iSCSI storage target with dual controllers (e.g. Dell MD3xxx-i series). And you wish to configure Windows iSCSI initiator with MPIO to enable multi-path connection for High Availability and Load Balancing. How should you go about it?
iSCSI Port Configuration
Let's begin with the iSCSI storage controller setup. Typically, each controller should have four iSCSI ports. Hence, you should configure 4 different VLANs on your iSCSI switches. Each port on each controller should connect to a VLAN (also an IP subnet). Jumbo frame (e.g. MTU 9000) is also recommended. Assign a valid IP address to each port. The port configuration should look something like this:
Create new LUN and assign the preferred path to either Controller
Typically, each LUN can only be accessed via a target controller at any one time. The connections to the preferred controller should be active and the other controller should be standby. Assign the new LUN to either preferred controller and remember its iSCSI port addresses.
Enabling MPIO on Windows host
Typically, each LUN can only be accessed via a target controller at any one time. The connections to the preferred controller should be active and the other controller should be standby. Assign the new LUN to either preferred controller and remember its iSCSI port addresses.
Enabling MPIO on Windows host
Similarly, configure the four or more iSCSI network connections (enable Jumbo Frame) on the Windows host. Install the necessary provider software given by the storage vendor. Add new Windows MPIO feature by executing "Install-WindowsFeature Multipath-IO -IncludeManagementTools" on Powershell. Activate MPIO and restart the host by clicking on the red boxes as follows:
Windows iSCSI Initiator
Start the Windows initiator by executing the command "iscsicpl". On Discovery tab, configure the Target Portals connecting to the iSCSI target directly. Go back to the Targets tab and click the "Connect" button.
By default, only 1 session connection is made. Disconnect the session. We can add more iSCSI sessions on clicking on the Properties button as above. Always check the "Enable multi-path" box whenever you see it.
Each session identifier represent each session to each controller. As you can see, I've already added two sessions to both controllers. You may add more by clicking on the "Add session" button. Check the "Enable multi-path" box and "Advanced" button. Assign the "Target portal IP" to the preferred controller address.
Multiple Connected Session (MCS) Policy
If you have more than 1 iSCSI NIC on the server for each session, click on the "MCS" button to add additional connections to each session. To add more connections to each session, click on the "Add" button and select the appropriate iSCSI initiator and target addresses.
Multiple Connected Session (MCS) Policy
If you have more than 1 iSCSI NIC on the server for each session, click on the "MCS" button to add additional connections to each session. To add more connections to each session, click on the "Add" button and select the appropriate iSCSI initiator and target addresses.
You can also choose a load-balancing algorithm. By default, simple "Round Robin" is used to distribute the loads evenly among the multi-paths.
Verify Multi-Path for each connected LUN
Click on "Device" and then "MPIO" button. Verify that each connected LUN can be accessed by more than 1 session.
Verify Multi-Path for each connected LUN
Click on "Device" and then "MPIO" button. Verify that each connected LUN can be accessed by more than 1 session.
Conclusion
In summary, there are two levels of path redundancy defined. Firstly, the session to each controller. Secondly, within a session, you can also have multiple connections defined under the MCS Policy. You may define different load-balancing algorithms for each level. In this setup, I clicked on the Device MPIO and defined "Failover-Only" for session level (remember the LUN can only be accessed via one controller at a time). Under each session, I defined "Round Robin" for multiple connections under MCS Policy for load-balancing.
In summary, there are two levels of path redundancy defined. Firstly, the session to each controller. Secondly, within a session, you can also have multiple connections defined under the MCS Policy. You may define different load-balancing algorithms for each level. In this setup, I clicked on the Device MPIO and defined "Failover-Only" for session level (remember the LUN can only be accessed via one controller at a time). Under each session, I defined "Round Robin" for multiple connections under MCS Policy for load-balancing.
