If you populate more than one Dimm per channel that will automaticaly decrease the bus speed. You will have more memory capacity but with a lower access. This is the balance you have to consider. For more information you can consult the article below and the user guide page 40:
<ADMIN NOTE: Broken link has been removed from this post by Dell>
Thanks for your reply. The first link you posted doesn't work (404 - not found):
<ADMIN NOTE: Broken link has been removed from this post by Dell>
If I look in the user manual on page 42, dual-rank RDIMMs have the same speeds for up to two modules per channel. The speed decreases when adding a third module. So, in this specific case (dual-rank RDIMMs with two modules per channel), there shouldn't be a decrease. Correct?
I still need clarification on my original question about the statement on page 43: Populate four DIMMs per processor (one DIMM per channel) at a time to maximize performance.
What happens if we only populate two DIMMs per processor? How does that affect performance? The manual doesn't explain how using four will "maximize performance" or what impact other combinations have.
I am not very architectural savvy person, so I'm not be able to provide detailed information. This is what I could understand from the requirement on the server, based on your question.
The chipset, Romley platform with Sandy Bridge processor, it now does the computing process, but also integrate the memory controller and the PCIe controller. Without the memory populated in each channel, it can't achive the intended performance. The Sandy Bridge EP is a two socket processor with four memory channels, each supporting up to three DIMMs per channel. Each EP processor supports 40 PCIe Gen3 lanes.
Though, I can't find any documentation that dual CPU can possible to have only 2 memory per CPU. The documentation has, minimum requirement of 4 memories per CPU, 1 in each channel.
Thanks for the response but that does not clarify the situation.
The documentation has, minimum requirement of 4 memories per CPU, 1 in each channel.
I'm assuming you mean "modules" when you write, "4 memories". There is not a minimum specified except that the memory configuration per-CPU must be identical.
Though, I can't find any documentation that dual CPU can possible to have only 2 memory per CPU.
Pages 45 and 46 of the manual give specific examples of such configurations, including mixed-size DIMMs. For example, page 46 lists:
16GB in A1, A2, A3, A4, B1, B2, B3, B4
8GB in A5, A6, B5, B6
The 8GB modules are grouped, two-per-CPU. However, it does not explain what this might do to performance.
Without the memory populated in each channel, it can't achive (sic) the intended performance.
Maybe documentation for the controller would be able to elaborate, if it exists.
The question remains: what is the actual performance impact of adding fewer than four modules per CPU?
Unfortunately, we don't have any documentation stating what are the performance impact with only populate only 2 slots. Are you having issues or errors when 2 slots are populated?
Dell-Stephane T
9 Legend
•
3.7K Posts
0
August 31st, 2020 03:00
Hi,
If you populate more than one Dimm per channel that will automaticaly decrease the bus speed. You will have more memory capacity but with a lower access. This is the balance you have to consider. For more information you can consult the article below and the user guide page 40:
<ADMIN NOTE: Broken link has been removed from this post by Dell>
https://topics-cdn.dell.com/pdf/poweredge-r720_owners-manual_en-us.pdf
Regards,
morjan
1 Rookie
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22 Posts
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August 31st, 2020 15:00
Hi Stéphane,
Thanks for your reply. The first link you posted doesn't work (404 - not found):
<ADMIN NOTE: Broken link has been removed from this post by Dell>
If I look in the user manual on page 42, dual-rank RDIMMs have the same speeds for up to two modules per channel. The speed decreases when adding a third module. So, in this specific case (dual-rank RDIMMs with two modules per channel), there shouldn't be a decrease. Correct?
I still need clarification on my original question about the statement on page 43:
Populate four DIMMs per processor (one DIMM per channel) at a time to maximize performance.
What happens if we only populate two DIMMs per processor? How does that affect performance? The manual doesn't explain how using four will "maximize performance" or what impact other combinations have.
-Jan
DELL-Joey C
Moderator
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4.1K Posts
0
August 31st, 2020 23:00
Hi,
I am not very architectural savvy person, so I'm not be able to provide detailed information. This is what I could understand from the requirement on the server, based on your question.
The chipset, Romley platform with Sandy Bridge processor, it now does the computing process, but also integrate the memory controller and the PCIe controller. Without the memory populated in each channel, it can't achive the intended performance. The Sandy Bridge EP is a two socket processor with four memory channels, each supporting up to three DIMMs per channel. Each EP processor supports 40 PCIe Gen3 lanes.
Though, I can't find any documentation that dual CPU can possible to have only 2 memory per CPU. The documentation has, minimum requirement of 4 memories per CPU, 1 in each channel.
Hope this clarifies.
morjan
1 Rookie
•
22 Posts
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September 4th, 2020 18:00
Hi Joey,
Thanks for the response but that does not clarify the situation.
The documentation has, minimum requirement of 4 memories per CPU, 1 in each channel.
I'm assuming you mean "modules" when you write, "4 memories". There is not a minimum specified except that the memory configuration per-CPU must be identical.
Though, I can't find any documentation that dual CPU can possible to have only 2 memory per CPU.
Pages 45 and 46 of the manual give specific examples of such configurations, including mixed-size DIMMs. For example, page 46 lists:
The 8GB modules are grouped, two-per-CPU. However, it does not explain what this might do to performance.
Without the memory populated in each channel, it can't achive (sic) the intended performance.
Maybe documentation for the controller would be able to elaborate, if it exists.
The question remains: what is the actual performance impact of adding fewer than four modules per CPU?
DELL-Joey C
Moderator
•
4.1K Posts
0
September 6th, 2020 21:00
Hi,
Unfortunately, we don't have any documentation stating what are the performance impact with only populate only 2 slots. Are you having issues or errors when 2 slots are populated?