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MSA2040 iSCSI DAC IP Addressing Query

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R S Burnell
Frequent Advisor

MSA2040 iSCSI DAC IP Addressing Query

We're setting up an MSA 2040 (10Gb iSCSI with Direct Attach Cables to 2 x hosts) and I'm not sure of how we should assign the IP addresses to the controller ports.


One document suggests that you should assign subnets vertically to the controller ports i.e. Controller A Port 1 and Controller B port 1 are on the same subnet then Controller A Port 2 and Controller B port 2 are on a different one.


If the above is true, then the first hosts iSCSI ports will both be on the same subnet as it will be conencted to port one on both controllers and the second host will have both of it's ports on the other subnet connected to ports 2 of both controllers?


I wold have expected that Controller A's ports would all be on one subnet and Controller B's on another so that both hosts conenct to both subnets?


Anyone got any thoughts on how this should be done?


Cheers for now




Valued Contributor

Re: MSA2040 iSCSI DAC IP Addressing Query

IMO direct attaching ISCSI means you're limiting your flexibility.

FC is a different matter, but I can't imagine what can be gained by direct attaching ISCI in real world configurations.

That is, unless there's a cost issue for not adding switches.

Are you limited to two hosts? Any chance of future expansion from an adding more hosts perspective?


As to your questions, for Direct Connect, theoretically,  the vertical subnetting allows for easier failover of the controller from the hosts perspective.

From the example in the manual you would assign IPs as such:

Controller A port 1:
Controller A port 2:
Controller A port 3:
Controller A port 4:
Controller B port 1:
Controller B port 2:
Controller B port 3:
Controller B port 4:

That is, Host#1  will be connected to ControllerA, Port 1 and ControllerB, Port 1 .

Also, Host#2  will be connected to ControllerA, Port 3 and ControllerB, Port 3 .

With MPIO enabled, the same LUN would be accessible via both controllers (ALUA) with redundancy.

But as you can see, they're all on the same subnet (


If need be, you can add , Host#3 which can be connected to ControllerA, Port 2 and ControllerB, Port 2 .

Also, Host#4  which can be connected to ControllerA, Port 4 and ControllerB, Port 4.


There other ways to do MPIO and /or ALUA, especially with switches.

R S Burnell
Frequent Advisor

Re: MSA2040 iSCSI DAC IP Addressing Query

Thanks for the information and it's waht we decided to configure and it works fine now.


We only have two physical servers connecting to the SAN so the DAC approach was cheaper and we can still add another 2 servers in the future should the need arise.


Cheers for now




Occasional Advisor

Re: MSA2040 iSCSI DAC IP Addressing Query

I've connected our 2040 up the same as you using 10Gb DAC cables. While some are keen to throw a switch inbetween the server hosts and the SAN, while that may be good for numerous host servers, if you have 4 or less cabled up the way you have which by the way is given as a recommended way to do it in the HP Best Practices publication, not having a pair of switches not only saves cash, but also removes several points of potential failure, as your setup only has 3 things to fail, the server, the DAC cables/SFP's and the SAN controller, compared to using switches that leaves the host server, double the DAC cables/SFP's (one set from the server to the switch and a second set from the switch to the SAN), the switches and the SAN controller!  Sometimes less is more.

See this document

in particular figure 21 on page 36 which sounds like how you have them setup


and page 32 in this document for the suggested IP address assignment


Note that a new version of 2040 firmware was released in the last few weeks that you may wish to update to as well. which you can get for the SFF rack from


and for the LFF version from


I reckon the v3 GUI leaves a lot to be desired and personally I find the older v2 much easier to use and more informative but maybe that's just me!