[Beowulf] building Infiniband 4x cluster questions

Vincent Diepeveen diep at xs4all.nl
Mon Nov 7 15:33:52 EST 2011


hi Greg,

Very useful info! I already was wondering about the different timings  
i see for infiniband,
but indeed it's the ConnectX that scores better in latency.

$289 on ebay but that's directly QDR then.

"ConnectX-2 Dual-Port VPI QDR Infiniband Mezzanine I/O Card for Dell  
PowerEdge M1000e-Series Blade Servers"

This 1.91 microseconds for a RDMA read is for a connectx. Not bad for  
Infiniband.
Only 50% slower in latency than quadrics which is pci-x of course.

Yet now needed is a cheap price for 'em :)

It seems indeed all the 'cheap' offers are the infinihost III DDR  
versions.

Regards,
Vincent

On Nov 7, 2011, at 9:21 PM, Greg Keller wrote:

>
>> 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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