[Beowulf] building Infiniband 4x cluster questions
Shainer at Mellanox.com
Mon Nov 7 17:07:51 EST 2011
RDMA read is a round trip operation and it is measured from host memory to host memory. I doubt if Quadrics had half of it for round trip operations measured from host memory to host memory. The PCI-X memory to card was around 0.7 by itself (one way)....
From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org] On Behalf Of Vincent Diepeveen
Sent: Monday, November 07, 2011 12:33 PM
To: Greg Keller
Cc: beowulf at beowulf.org
Subject: Re: [Beowulf] building Infiniband 4x cluster questions
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.
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
>> 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?!
>> 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
>>>> 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:
>>>> 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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