[Beowulf] Questions about upgrading InfiniBand

Gilad Shainer Shainer at Mellanox.com
Wed Apr 18 12:07:33 PDT 2012

> Gilad,
> Thanks for the quick, helpful responses. See my in-line comments below.

Thanks for the comments. 

> On 04/18/2012 11:27 AM, Gilad Shainer wrote:
> >> Beowulfers,
> >>
> >> I'm planning on adding some upgrades to my existing cluster, which
> >> has
> >> 66 compute nodes pluss the head node. Networking consists of a Cisco
> >> 7012 IB switch with 6 out of 12 line cards installed, giving me a
> >> capacity of 72 DDR ports, expandable to 144, and two 40-port ethernet
> >> switches that have only six extra ports between them.
> >>
> >> I'd like to add a Lustre filesystem (over InfiniBand)  to my cluster,
> >> and then begin adding/replacing nodes in the cluster. Obviously, I'll
> >> need to increase capacity of both my IB and ethernet networks. The
> >> questions I have are about upgrading my InifiniBand.
> >>
> >> 1. It looks like QLogic is out of the InfiniBand business. Is
> >> Mellanox the only game in town these days?
> > Intel bought the QLogic InfiniBand business so this is a second option
> I searched both the QLogic and Intel websites for 'InfiniBand", and neither
> returned any hits yesterday. It makes sense that you can't find any IB info on
> QLogic's site anymore. Today, I was able to find the Link for Intel TrueScale
> InfiniBand products. Intel did a good job of hiding/burying the link under
> "More Products" on their Products pull-down menu. No idea why I couldn't
> find it by searching yesterday.
> Typo in search box, maybe?
> >
> >> 2. Due to the size of my cluster, it looks like buying a just a
> >> core/enterprise IB switch with capacity for ~100 ports is the best
> >> option (I don't expect my cluster to go much bigger than this in the
> >> next 4-5 years).  Based on that criteria, it looks like the Mellanox
> >> IS5100 is my only option. Am I over looking other options?
> > You can also take 36 port switches, few more cables, and build the desired
> network size (for example  for Fat Tree topology). It is easy to do, might be
> more cost effective. If you need help to design the topology (which ports
> connects to which port, I can send you a description). With this option, you
> can also do any kind of oversubscription if you want to.
> I was looking into a fat-tree topology yesterday. Considering the number of
> additional switches needed, and the cabling costs, I'm not sure it will really
> be cost effective. Just to stay at the same capacity I'm at now, 72 ports, I'd
> need to by 6 switches + cables.

It depends on the system that you have, cable distance etc. In most cases it can be more cost effective, but it is easier to use one large switch. In any case, if you need help to find the best option, email me the topology

> >
> >>
> http://www.mellanox.com/content/pages.php?pg=products_dyn&product_
> >> family=71&menu_section=49
> >>
> >> 3. In my searching yesterday, I didn't find any FDR core/enterprise
> >> switches with > 36 ports, other than the Mellanox SX6536. At 648
> >> ports, the SX6536is too big for my needs. I've got to be over looking other
> products, right?
> >>
> >>
> http://www.mellanox.com/content/pages.php?pg=products_dyn&product_
> >> family=122&menu_section=49
> > More options are getting out now. 324-port version will be available in a
> week, and the 216 few weeks after. Before the summer that 108 will be
> released.
> That's in my timeframe, so I'll keep an eye on the Mellanox website.

Sure. Feel free to email me directly, and I can connect you to the folks that can help

> >
> >> 4. Adding an additional line card to my existing switch looks like it
> >> will cost me only ~$5,000, and give me the additional capacity I'll
> >> need for the next 1-
> >> 2 years. I'm thinking it makes sense to do that, and wait for
> >> affordable FDR switches to come out with the port count I'm looking
> >> for instead of upgrading to QDR right now, and start buying hardware
> >> with FDR HCAs in preparation for that.  Please feel free to
> >> agree/disagree. This brings me to my next question...
> > Depends what you want to build. You can take FDR today, build 2:1
> oversubscription to get "QDR" throughput and this will be cheaper than
> using QDR switches. In any case, if you need any help on the negotiation
> side, let me know.
> Thanks for the offer. If I decide to buy new switches instead of expanding my
> DDR switch, i'll e-mail you off-list.
> >
> >> 5. FDR and QDR should be backwards compatible with my existing DDR
> >> hardware, but how exactly does work? If I have, say an FDR switch
> >> with a mixture of FDR, QDR, and DDR HCAs, will the whole fabric slow
> >> down to the lowest-common denominator, or will the slow-down be
> based
> >> on the two nodes involved in the communication only? When I googled
> >> for an answer, all I found were marketing documents that guaranteed
> >> backwards compatibility, but didn't go to this level of detail, I
> >> searched the standard spec (v1.2.1), and didn't find an obvious answer to
> this question.
> > You can mix and match anything on the InfiniBand side. You can connect
> SDR, DDR, QDR and FDR and it all will work. When you do that, a direct
> connection between 2 ports will be run at the common denominator. So if
> you have FDR port connected to FDR port directly, it will run FDR. If you have
> DDR port connected directly to FDR port, that connection will run DDR. In
> your case, part of the fabric will run FDR, part will run DDR.
> That's what I suspected. Thanks for the confirmation.
> >
> >
> >> 6. I see some Mellanox docs saying their FDR switches are compliant
> >> with
> >> v1.3 of the standard, but the latest version available for download
> >> is 1.2.1. I take it the final version of 1.3 hasn't been ratified yet. Is that
> correct?
> >
> > 1.3 is the IBTA spec that includes FDR and EDR. The spec is completed, but
> not on the web site yet.
> Ditto.
> --
> Prentice

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