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I just had a few questions related to the networking side of our infrastructure. We are about to move to a new building and we get a mostly new data center. We are taking all our hosts (3) but we are getting all new switches. Some of the questions i have are related to our SAN, and maximizing performance. We currently have an IBM N3600 (AKA - NETAPP) iSCSI SAN. There are two QLogic HBA's in each host and we are nning VSphere on all hosts. Since we are getting all new switches we were going to plan ahead and make everything 10GB at least on the backbone. I'm curious what the throughput is of those iSCSI HBA's is since i think this is going to be our slowing point, or will it be the hard drives? Is there anything we can do to the SAN and/or the Hosts to maximize perormance to our network? It seems pointless at this time to invest all the money into 10GB if our SAN can't even keep up. If anyone has any suggestions about how to maximize this new isntall i would really appreciate the input. Thanks

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You don't mention the particular QLogic iSCSI HBAs - we'll need to know that. – Chopper3 Jan 13 '10 at 13:41
How many drives do you have in each of the LUNS on the SAN? This will be the biggest bottleneck for throughput on a SAN. – Scott Lundberg Jan 13 '10 at 14:45

I've a HUGE fan of using less 10Gps ports than more 1Gbps ports for modern server installations assuming you're happy to deal with firewalling the trunked VLANs this implies.

As for hitting a full 10Gbps, well to be honest not many boxes can get the full use of these links but importantly many servers can use >2Gbps, especially when using TOE and iSCSI-accelerated NICs/HBAs/CNAs. But of course you need to deal with the full data path - it's no point 10gig'ing your servers and switches if your storage can't cope and your N3600 only has 4 x 1Gbps NICs (iirc).

If you have >1Gbps of server to server or server to client traffic then I'd suggest going to 10Gig today but I'm not that sure that you'll get that much benefit from the iSCSI unless you plan it well.

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Are your iscsi hba's 1gig or 10gig hba's?

But some general suggestions.

  • Make sure you have jumbo frames enabled on the filer, the switch and your vsphere hosts.

  • Make sure you have your virtual guests partitions aligned properly. Do a google on netapp partition alignment and read up if you aren't already familiar with.

Another thing you'll want to know before the move is, Are your hosts even fully utilizing and pushing your 1gig (I'm assuming) iscsi network throughput. If they aren't doing this then 10gigs isn't really going to do much.

On the filer end of things, check to see how hard it's being pushed right now. Does your filer even have 10gig cards in it?


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The NetApp technical library is a good resource as well. is a little dated, but talks about iSCSI Performance Options. There’s also as well as other reports on NetApp and VMware best practices that may help in sorting out the design.

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