8GB RDIMM Ram for D20 and C20x

[gpsd]

I know the FRU for the 8GB RDIMMs for the D20 and C20x, but wondered if anyone knows whether the following 8GB RDIMM would function just as well - 67Y1464-02. I only ask because I can get this part number for about 1/3 the price of the one listed for the D20 and C20x. The only difference I can see is that this one is 2rx4 and the 8gb RDIMM listed for the D20 and C20x is 4rx4 (so twice the depth, I think). But many of the other modules accepted by the D20 C20x are 2rx4 (but just not the 8gb one. Thanks in advance for any input.

George

[gpsd]

Correction - these do not have heat spreaders on them (but I do have the chillers already).

[erik Community SuperMod]

welcome to the forum!

there are quite a few dual- and quad-rank 8GB RDIMMs qualified for the intel 5520 chipset.

67Y1464 is a valid part number.   67Y1464-02 is something vendor-specific, adding the -02 either due to being open-box, "refurbished" (which is impossible with memory and instead should designate recertification), or designating a specific warehouse source.   given that, a quick search finds this listing at codemicro.com.   companies like this source parts from various warehouses, pointing toward the -02 tacked onto the part number.

regarding the part itself, it should be a 2Rx4 8GB RDIMM.   i can't find whether or not it has heat spreaders but would suspect that they do despite the samsung part number listed on codemicro's site.   i've not personally seen an RDIMM FRU without spreaders but wouldn't doubt they're out there.   while they help keep the modules cooler under heavy load, most people don't push their memory hard enough for it to matter.   fwiw, my 4GB RDIMMs have heat spreaders.

[gpsd]

Thanks Erik, and yes, sorry, meant to exclude the "-02" so as not to confuse - they are new, open box with full warranty and $100 per RDIMM. So I take it these will probably work.

I was always under the impression that quad-ranked were less desirable than dual-ranked (and supposedly less expensive to manufacture). Is this still the case - I currently have single processor X5650?

Also, I understand that dual and quad ranked can be mixed, but I don't know anyone who has had first hand experience (and again I ask because I already have two of the properly speced Lenovo quad-ranked 8gb RDIMMs).

Regards,

George

[erik Community SuperMod]

i'm not sure about mixing RDIMM ranks.   with FB-DIMMs, different ranks didn't always play well together and some ranks didn't play at all.   but, since you're looking at original lenovo parts, i'd venture to guess that the units you're looking at will work just fine.   buy from a reseller offering fair returns and you'll be ok.

without seeing these modules in person, i don't know whether they're dual or quad.   they might actually be quad.

[gpsd]

According to this, they are dual ranked: http://www.samsung.com/global/system/business/semiconductor/family/2010/1/1/ddr3_product_guide_oct_0...

Any thoughts on pros or cons with dual- versus quad-ranked. But best description I ever read was a blog from 2009 relating to Xeons in Sun workstations and servers. The suggestion then was that dual ranked was a much better performer than quad ranked. Not sure if that is the case any longer though.

[erik Community SuperMod]

after doing some homework this morning, i came across the following report from fujitsu:

https://sp.ts.fujitsu.com/dmsp/docs/wp-westmere-ep-memory-performance-ww-en.pdf

page 17 mentions the following:

"A second advantage of dual and quad-rank modules is the physical reason already discussed. Memory cells are arranged in two dimensions. A line is opened and then a column item is read in this line. While the line (more commonly called page) is open, further column values can be read with a much lower latency. This latency difference motivates optimization of the memory controller which reallocates the pending orders regarding possible "open" memory pages. With dual and quad-rank modules, the probability of accessing an open page increases."

unfortunately they don't mention any specific data.   given the scope of the paper, i'm actually surprised they didn't test bandwidth between modules of equal size and different rank.   i'd like to know the answer to this myself.

(edit: typo)

[gpsd]

Yes, it is very confusing, particularly with the limited information that seems to be out there.

From what I understand though, double and quad ranked are only desirable where you have large amounts of ram (and DIMMS), as only one rank can be accessed at a time for read or write as all ranks on a DIMM share the same data bus (64 bit for regular DIMMS and 72 bit for RDIMMS, I think). So different ranks on different DIMMS can be accessed but not different ranks on the same DIMM. Not sure I am completely on the mark, but it is something like that. Supposedly it affects the real world speed of the ram.

[psuturtle Lenovo Staff]

Quad ranked will work.  When we originally developed the D20 platform, the only way you could even get 8GB RDIMMs was with quad ranked parts.  So they'll work, but I'd caution against using them if you're on a Nehalem based Processor (E55xx or X55xx series Xeons).  If you use quad ranked memory in a two DIMM per channel (2DPC) configuration with Nehalem CPUs, they will slow down your memory speed one bin.  So if your RDIMMs were QR 1333MHz in 2DPC, they'll actually run at 1066MHz (1066MHz QR in 2DPC would run at 800MHz). 

Again, this is only for Nehalem based systems.  This restriction goes away if you're using Westmere (56xx series).  You can thank Intel for all of this

I'd personally go with the dual rank.  They'll generally run a little cooler, and are likely newer parts than the quads.

A couple of the big vendors are now running their RDIMMs without integrated heatspreaders.  I've got 16GB RDIMMs without spreaders on them.  Many of my 8GB RDIMMs are bare.  However, make sure you're still running your memory coolers, as they are required if you have any 4GB (or higher) RDIMMs installed.

[gpsd]

Hi psuturtle,

Thanks for the info. But the quad-ranked 8GB RDIMMS are the ones specced for the D20 and C20x. The dual ranked 8GB RDIMMS I was asking about are technichally specced for the Thinkserver, but they look like they should work. 

Also, what areyour thoughts on mixing dual and quad ranked RDIMMS in the same bank?

Thanks,

George