Re: 4-way Opteron vs. Xeon-IBM X3 architecture

On Mon, 2 Jan 2006 18:00:53 +0000 (UTC), David Wang <foo@xxxxxxxxxxx>
wrote:

>George Macdonald <fammacd=!SPAM^nothanks@xxxxxxxxxxxxx> wrote:
>> On Fri, 30 Dec 2005 20:51:42 +0000 (UTC), David Wang <foo@xxxxxxxxxxx>
>> wrote:
>
>> >The point here is that the issue concerns both speed AND capacity.
>> >The references given suggest that higher speeds are possible, but
>> >none shows that higher speeds are possible with full capacity.
>
>> Depends what you mean by "full capacity" - if you mean eight quad-rank
>> DIMMs then the memory mfrs don't even make PC3200 in that form factor; if
>> you look at the mbrds available to us, eight slots per CPU is not something
>> I've seen. OTOH right in this thread is a "reference"
>> 11r8donj9u00g9d@xxxxxxxxxxxxxxxxxx apparently demonstrating PC3200
>> operation with 72 devices per channel.
>
>I've already defined what I meant by "full capacity". 4 ranks of
>DRAM devices, 18 devices per rank, 72 devices per channel running
>at 400 Mb/s.
>
>As to the reference, the message header points right back in this thread,
>and there's nothing in that post that shows 72 devices per channel @
>400 Mb/s.

What is this - myopia?... denial? Rob has 2x Crucial 2GB RDIMMs on each
channel. I'd have thought you'd be able to figure it out. Are you even
reading what I've said?... that the reference was to a post in this
thread... or are you just shooting from the hip?

>> >As you may suspect, I read plenty about memory systems, and I would
>> >vigorously challenge your memory in regards to the "common knowledge"
>> >here. I do not believe it's common knowledge for anyone to have
>> >demonstrated running 64 DDR(1) SDRAM devices reliabliably @ 400 Mb/s.
>> >If you can, please do cite a concrete reference URL. What you remember
>> >to have seen may not actually be what it is.
>
>> See above.
>
>There's nothing in the referenced post.

I think you can do better than that.

>> >The issue that prohibits making the higher speed version with x4 devices
>> >is that you have to hang 16 of them (18 with ECC) on the same address
>> >and command busses per rank. That's a rather heavy electrical load to
>> >run @ 200 MHz. So, no, you can't just look at "enthusiast memory" built
>> >with x8 parts and automatically assume that x4 parts will work just the
>> >same at the same data rate, because you're going to need even faster
>> >parts to meet the same timing.
>
>> The memory mfrs are producing PC3200 2GB RDIMMs with 36 devices.<shrug>
>
>You need them to make PC3200 4 GB RDIMMs with 36 devices and work in the
>2 slot boards to get to 8 GB per channel and 16 GB per CPU. Once you have
>that, then you can raise the memory capacity of the 4P Opteron box to
>64 GB. Until then, the limit for the 4P Opteron box remains as 32 GB of
>DDR(1) @ 400 Mb/s.

Ah, it's denial.

>> >Because you cited some rather nebulous references in regards to memory
>> >from the enthusiast market and assumed that it would work in the server
>> >world. I was simply pointing out that's not going to work here because
>> >of configuration differences and electrical loading considerations.
>
>> AMD has specs. They can be exceeded and have been regularly for Athlon64
>> unbuffered operation; it does seem that the specs for Opteron registered
>> could be and in fact are easily exceeded.
>
>No one running a 4P server and using it commercially will run the box with
>memory system configuration that exceeds spec.

If the spec is 3-years old and the devices and assemblies have improved,
there's no reason not to. To deliberately igniore technology progress is
perverse.

>> >Which is what is shipping in HP's Opteron server, and guarenteed to
>> >work by HP. That guarentee provides the effective upper limit to
>> >the maximum memory capacity of an Opteron server as of today. That
>> >limit cannot be exceeded or changed arbitrarily. This, I believe was
>> >the crux of the contentious point. . .
>
>> The original claim was that anything "> half-loaded" required a decrease in
>> clock speed; even AMD specs go above half-loaded.
>
>That claim is supported by the specification of a validated, shipping
>system. Your argument that the server folks can run with more memory
>in the memory system by pushing the configuration beyond the validated
>spec - does not hold water.

No pushing, or water, is required. If mfrs want to derate AMD's specs
that's up to them.

>
>> Every DIMM mfr is selling unbuffered boutique parts rated at PC4000/DDR500
>> (2.8V seems the norm) - where they get the chips from matters not...
>> whether it violates some enshrined, 3-year-old JEDEC document is of no
>> importance to the people selling or buying.
>
>No one buys these parts to put in a 4P Opteron/Xeon server, and the
>sentiment does not apply.

There you go again trying to suggest that I said something I didn't. I
thought it seemed perfectly obvious here and in my previous mention of
those PC4000 DIMMs that the fact that such devices are available, means
that higher performing devices can be used for servers. I'm getting tired
of repeating myself here.

>> >They'll enable servers with incredible amount of memory, and the power
>> >headache that comes with it. The AMB is just part of the problem. With
>> >16 device per FBD, you can get the ratio of AMB device power to DRAM
>> >device power down to 15~20%.
>
>> But the AMB power usage must depend on its position in the channel... so
>> are they going to be able to be able to lose the heatpipes on them?:-)
>> Surely the Primary is always going to get hammered.
>
>Heatpipes? From what I've seen, it's just a small heatsink. I think
>it's about ~4W per fully-on AMB, and you can selectively turn off
>parts of it to save power.

This
http://www.tecchannel.de/_misc/img/detailoriginal.cfm?pk=346982&fk=432957&id=il-74145445969594731
is what I'd call a heatpipe heatsink and it is *not* small in relation to
the part. Other sources have commented on the heat problem and people
don't normally put fans over devices which are not hot - you'll need to do
more than think... like maybe burn your finger on the thing.

--
Rgds, George Macdonald
.

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