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I'm doing some experiment with iSCSI MPIO between FreeNAS 9.3 and two XenServer 6.5 hosts. I would like to use iSCSI MPIO to serve as VM storage. Pretty common environment, but without a switch to reduce the cost of the solution and minimize the overhead added by a switch on the iSCSI network.

The architecture is the following: There are 10x GigE interfaces on the FreeNAS Server, two integrated intel boards on the motherboard and two 4x GigE combo cards.

I've created /30 links between the combo cards and the two XenServer hosts, in the following way:

Connection to Host #1:
igb0: 192.168.10.1/30
igb4: 192.168.11.1/30

Connection to Host #2:
igb1: 192.168.20.1/30
igb5: 192.168.21.1/30

As you can see it's pretty explicative, the XenServer hosts have the following matched IP's:

192.168.10.2/30
192.168.11.2/30
192.168.20.2/30
192.168.21.2/30

But here the problem starts. I cannot start an iSCSI connection with a Portal with those 4 addresses. It fails when searching for the LUN, during the IQN phase. If I completely forget about the 192.168.20.1,192.168.21.1 IP addresses, I can find the LUN, but host #2 will be without an iSCSI network, since the 192.168.10.0/30 and 192.168.11.0/30 networks are unreachable. They are point-to-point links.

According the FreeNAS documentation I can create multiple portals. Which appears to be a solution, but I've tried to do this without success. I cannot map the same LUN on different portals, so it impossible.

Another solution would be using more than one IP on the same subnet on the FreeNAS box, but as all we know this is broken TCP networking.

The last effort is to create the XenServer iSCSI SR over the CLI with a very specific setting. But I wasn't able to try this by myself.

  • From the xen, can you ping the freenas? – yagmoth555 Feb 13 '15 at 0:13
  • Yep, for sure. On all the interfaces accordingly to the host. XenServer #1 pings 192.168.10.1 and 192.168.11.1, while XenServer #2 pings 192.168.20.1 and 192.168.21.1. – Vinícius Ferrão Feb 13 '15 at 3:03
  • If it's a shared storage between your xen, I assume the target IP must be in the same range on both xen. – yagmoth555 Feb 13 '15 at 3:08
  • Yeah, I would assume this as a limitation, one that I wasn't aware. It's possible to build an Multipath'd iSCSI with VMware ESXi, so I'm trying to do the exactly same thing. The major problem here is the lack of manual controls for SR discovery and manipulation. – Vinícius Ferrão Feb 13 '15 at 13:27
  • Yeah, as when in a pool, you issue the create sr command via the xencenter, and it try on both server with the same target IP. On the freenas can you put some port in switch/bridge mode in example (Iam not a linux expert), that would resolve your issue, as you can directly plug the xen after with just different ip in the same LAN. – yagmoth555 Feb 13 '15 at 13:33

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