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In my server lab, I am running a vCenter cluster with 2 ISCSI targets. Both of these are directly connected to switch using SFP+ port.

I assume, when I do such a process as cloning a VM from one datastore to another (say ISCSI 1 -> ISCSI 2), the traffic would flow ISCSI 1 directly to ISCSI 2 ( ISCSI 1 SFP+ -> switch -> ISCSI 2 SFP+). I think the above is how it works based on common sense, however, if I am wrong please let me know.

I would like to increase the bandwidth between both ISCSI instances. However, the switch only supports 2 SFP+ ports, while each ISCSI has 2 available SFP+ ports(4 total). My question is, is it possible to perhaps increase bandwidth between 2 ISCSI targets by directly plugging them into each other on their secondary SFP+ cables while keeping the initial SFP+ cables where they are at(so the vHosts can actually reach ISCSI targets)? That way VMs could to be transferred over both SFP+ ports:

1) ISCSI 1 SFP+ -> switch -> ISCSI 2 SFP+ 2) ISCSI 1 SFP+ -> ISCSI 2 SFP+

I am not too sure if ISCSI can support such a thing, or if networking, in general, can support this, so please let me know about potential solutions to this problem.

Aibek
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If you clone a VM from one iSCSI Storage (Target) to another, then the ESXi Server reads the VM from the Source Lun and writes it to the Target Lun. The Storages don't communicate directly with each other, so a direct connection does not help.

Alexander Worlitschek
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  • Got it, thanks for clarifying. Do you know of a good way to get around such a (In my opinion) "limitation"? – Aibek Jan 28 '20 at 12:47
  • This is not that easy without information. At first i would try to locate the problem. Are the two SFP+ network links really saturated, or is it the iscsi interface on the ESXi host. What's about the storage performance. Is there a bottleneck? – Alexander Worlitschek Jan 28 '20 at 13:05
  • Thank you for you insight, I will take a look at that! – Aibek Jan 28 '20 at 13:25
  • Out of curiosity, when I only have 1 ISCSI, and I clone a VM that will end up on the same ISCSI, would it take the same path, or would it be more efficient(aka don't go thru ESXi and copy directly)? – Aibek Jan 29 '20 at 05:00
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    I you have one iscsi storage and clone a VM, then it depends if the storage has vaai support. If this is the case, the vm can be copied directly on the storage and no data traffic has to go over the network links. – Alexander Worlitschek Jan 30 '20 at 08:36