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

On Tue, 3 Jan 2006 06:08:39 +0000 (UTC), David Wang <foo@xxxxxxxxxxx>
wrote:

>George Macdonald <fammacd=!SPAM^nothanks@xxxxxxxxxxxxx> wrote:
>> On Mon, 2 Jan 2006 18:00:53 +0000 (UTC), David Wang <foo@xxxxxxxxxxx>
>> wrote:
>
>> >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?
>
>Rob has 2 2-GB RDIMMs per channel. This gets him 4 GB per channel and
>8 GB per CPU.
>
>This is the same configuration as the 32 GB per 4P Opteron box @ 400 Mb/s
>configuration that you believed to be limited.

No it is NOT - it is 4 full ranks of 18x 512Mb devices each, which has
repeatedly been claimed to not work at PC3200 by Kanter... & you, just 4
paras above.

>I had thought that Rob's difficulty in configuring even this setup with
>mixed RDIMMs would go some ways in convincing you that you don't just
>throw 8 GB of DDR(1) memory per channel into an Opteron box and expect
>it to work @ 400 Mb/s - apparently I was incorrect in expecting you see
>that the two configurations are equivalent.

This is unbelievable - you've been harping on about 64/72 devices per
channel and when presented with the concrete evidence that it does work at
PC3200, you wriggle with some imagined claim of mine... some ethereal 8GB
you dreamt up. The only thing "incorrect" is your persistent changing of
the "target".

As for mixing different mfr DIMMs, I don't see any "difficulties" here at
all - just another imagined "fact"; that is well known to be a less than
optimal way of going about getting speed and capacity - it has been, to a
certain extent, since PC-133 SDRAM, and with DDR-SDRAM it's a very risky
proposition and not something I'd expect to work well. The way I read it
Rob was experimenting just to see but was happy to use a single memory mfr
per mbrd.

>> >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.
>
>It's simple mathematics. You stated that more DDR(1) memory can be crammed
>into the 4P Opteron server @ 400 Mb/s. You need 2 4-GB DIMMs with 36 1 Gb
>DRAM devices per DIMM to get that done.

No it's not mathematics - it's arithmetic... even simpler: Micron does not
have DDR400 1Gb devices... yet; the 2GB RDIMMs in question have 18x 512Mb
devices per side... two double sided DIMMs... four full ranks per
channel... 72 devices. It couldn't be clearer.

>> >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.
>
>Reliability considerations trumps everything in the traditional medium/
>heavy duty server segment. You don't throw parts that have not gone through
>many device-years of qualification into the nearest server box.

Oh damn the traditional - the results are in.

>> >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.
>
>Which means 32 GB in the 4P Opteron box is as good as it gets (for now,
>until DDR2 parts arrive), and your previous assertions in regards to
>HP Opteron's memory capacity @ 400 Mb/s is not valid.

The 32GB exceeds AMD's specs... if you'd only look. To go higher you need
1Gb parts with DDR400 rating or quad-rank RDIMMs which are only qualified
up to DDR333... that I've seen.

>> >> 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.
>
>The over spec'ed parts are never going to end up in a server. Power
>increases proportional to square of the voltage. In big servers packed
>with DRAM devices, you're not going to want to increase memory capacity
>by cranking up the voltage to get the performance, even assuming you
>can get such a memory system to qualify.

They're only over-spec'd by your 3-year old rulebook. In fact they work
fine by all accounts in desktops and workstations and the mfr makes the
specs.

>You derided FBD's for the power consumption of the AMB, yet somehow
>power increase to shoehorn overspec'ed memory into a server box is
>acceptable?

You read what I said as derision - your choice... reading my irony vs.
your derision on Micron as criticism of FBDIMM is err, contorted logic from
my POV. I was originally optimistic about FBDIMMs but when I see what's
available this late in the game, I'm beginning to wonder about them. It
seems that Intel, in its desperation to catch up, might be jumping the gun.

As for power problems, .2V extra is hardly comparable at this stage of the
DDR1 game and it's not a given that it would be required at PC3200... just
the better qualified devices. Hell, power supplies can be out by that much
anyway.

>It's not going to happen, and your repeated reference in bringing
>the overspec'ed parts into a discussion about server memory is
>distracting to say the least.

I hope it's as distracting as your persistent changing of the framework and
"target" of the discussion.

>> >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.
>
>"Heatpipe" has specific connectation, and it does not apply here. That is
>a small clip on heatsink.

More "Wang's rules".Ô_ô I do not know what connectation means but if it
has pipes (capillary tubes actually) filled with a liquid/vapor phase
coolant inside, it's a heatpipe. You can apply some personal
"connectation" for your own view of things - you cannot impose it on other
people.

--
Rgds, George Macdonald
.

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