[Beowulf] building Infiniband 4x cluster questions

Greg Keller Greg at Keller.net
Mon Nov 7 12:21:51 PST 2011


> Date: Mon, 07 Nov 2011 13:16:00 -0500
> From: Prentice Bisbal<prentice at ias.edu>
> Subject: Re: [Beowulf] building Infiniband 4x cluster questions
> Cc: Beowulf Mailing List<beowulf at beowulf.org>
> Message-ID:<4EB82060.3050300 at ias.edu>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Vincent,
>
> Don't forget that between SDR and QDR, there is DDR.  If SDR is too
> slow, and QDR is too expensive, DDR might be just right.
And for DDR a key thing is, when latency matters, "ConnectX" DDR is much 
better than the earlier "Infinihost III" DDR cards.  We have 100's of 
each and the ConnectX make a large impact for some codes.  Although 
nearly antique now, we actually have plans for the ConnectX cards in yet 
another round of updated systems.  This is the 3rd Generation system I 
have been able to re-use the cards in (Harperton, Nehalem, and now 
Single Socket Sandy Bridge), which makes me very happy.  A great 
investment that will likely live until PCI-Gen3 slots are the norm.
--
Da Bears?!

> --
> Goldilocks
>
>
> On 11/07/2011 11:58 AM, Vincent Diepeveen wrote:
>> >  hi Prentice,
>> >
>> >  I had noticed the diff between SDR up to QDR,
>> >  the SDR cards are affordable, the QDR isn't.
>> >
>> >  The SDR's are all $50-$75 on ebay now. The QDR's i didn't find cheap
>> >  prices in that pricerange yet.
>> >
>> >  If i would want to build a network that's low latency and had a budget
>> >  of $800 or so a node of course i would
>> >  build a dolphin SCI network, as that's probably the fastest latency
>> >  card sold for a $675 or so a piece.
>> >
>> >  I do not really see a rival latency wise to Dolphin there. I bet most
>> >  manufacturers selling clusters don't use
>> >  it as they can make $100 more profit or so selling other networking
>> >  stuff, and universities usually swallow that.
>> >
>> >  So price total dominates the network. As it seems now infiniband 4x is
>> >  not going to offer enough performance.
>> >  The one-way pingpong latencies over a switch that i see of it, are not
>> >  very convincing. I see remote writes to RAM
>> >  are like nearly 10 microseconds for 4x infiniband and that card is the
>> >  only one affordable.
>> >
>> >  The old QM400's i have here are one-way pingpong 2.1 us or so, and
>> >  QM500-B's are plentyful on the net (of course big disadvantage: needs
>> >  pci-x),
>> >  which are a 1.3 us or so there and have SHMEM. Not seeing a cheap
>> >  switch for the QM500's though nor cables.
>> >
>> >  You see price really dominates everything here. Small cheap nodes you
>> >  cannot build if the port price, thanks to expensive network card,
>> >  more than doubles.
>> >
>> >  Power is not the real concern for now - if a factory already burns a
>> >  couple of hundreds of megawatts, a small cluster somewhere on the
>> >  attick eating
>> >  a few kilowatts is not really a problem:)
>> >



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