apologies for the long-winded post in advance...

Attempting to troubleshoot some iSCSI sluggishness on a brand new vSphere deployment (still in test).

Layout is as such:

3 VSphere hosts, each with 2x 10GB NICs plugged into a pair of Nexus 5020s with a 10gig back-to-back between them. NICs are port-channeled in an active/active redundant fashion (using vPC-mac pinning for those of you familiar with N1KV) Both NICs carry service console, vmotion, iSCSI, and guest traffic. iSCSI is on a single subnet/single VLAN that is not routed through our IP network (strictly layer2)

Had this been a 1gig deployment, we probably would have split the iSCSI traffic off onto separate NICs, but the price/port gets rather ridiculous when you start throwing 4+ NICs to a server in a 10gigabit infrastructure, and I'm not really convinced it's necessary. Open to dialogue/tech facts re: this, though.

At this point even a single VM guest will boot slowly to iSCSI storage (EMC CX4 on the same Nexus 5020 10gig switches), and restores of VMs from iSCSI take about twice as long as we'd expect them to. Our server folks mentioned that if we split the iSCSI off onto its own NIC, performance seems significantly better. From a network perspective, I've run through the variables I can think of (port configuration errors, MTU problems, congestion etc.) and I'm coming up dry. There really is no other traffic on these hosts other than the very specific test being performed at the time. Important thing to note is that guest traffic works just fine... it seems storage is the only thing affected by whatever gremlin exists.

Concluding that we're not 'overutilizing' the network infrastructure since we're doing hardly anything, I'm just looking for some helpful tips/ideas we can use to resolve this... preferably without hurling extra 10gig NICs that are going to sit around 10% utilization while we've got 70+% left on our others.

1 Answer 1


Presumably you have one or more of the dual-port 10Gbps adapters in your CX4? if so have you tried a point-to-point link between one of the ports and a single server for baseline performance tests? If not then I'd think about stringing that up, cut out the nexus's and see how you get on - results should be interesting.

Oh and as an aside your design seems fine to me ;)

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