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April 30th, 2025 23:20
2RX4 vs 2RX8 DIMM Question. Vendor put different DIMM type than the Manual specifies for the config
I just bought a used R730 LFF from a reseller. It is replacing an R710 for light use in a very small office environment. It will be an ESXi host for about five VM's: vCenter, a Shoretel phone server (two users, three trunks), and a few other miscellaneous VM's.
The machine has dual E5-2680v4 CPUs. I updated BIOS and firmware to the latest.
The vendor shipped it with 96GB of 2RX4 DDR4 2400 DIMMs. The manual does not list that as a supported memory configuration for two reasons.
(For 96GB, the manual does not list 16GB DIMMs with dual CPUs--it lists either 4GB or 8GB DIMMs. The manual does list 16GB DIMMs for a 128GB configuration. I will buy two extra DIMMs to remedy that and use all four memory channels.)
Here is the pending question: For dual CPUs with 128GB, the manual specifies only 2RX8 for 16GB DIMMs. In fact, the manual specifies 2RX8 for every memory configuration using 16GB DIMMs.
I raised this with the vendor and he says that it makes no difference and that they configure severs all the time using either 2RX4 or 2RX8. (Interchangeably, using one or the other for the same model Dell servers.)
I can only go by what the manual says but the vendor dismissed it out of hand. "We do it all the time" is not very convincing to me, particularly since the manual asserts otherwise.
What effect will there be from using 2RX4 16GB DIMMs in this machine? I imagine Dell had a reason to specify 2RX8 with this config. I've searched a lot of articles and posts and not found anything on point. I found plenty of threads about not mixing types. Others about whether dual or single rank are specified. A few threads pointed to dead links.
Can anyone elaborate? Would it have an effect on the performance of the RAM? If there is any downside to using 2RX4 in this config, I will insist on the 2RX8.
The vendor was getting annoyed that I brought it up. In the end, it sounded like he would swap the RAM. Given his hard pushback, that's not guaranteed and I'd like to have as much info as I can.
(A secondary reason for wanting the RAM swapped is that I wanted it to match the R730xd machine being used for backups (and as backup host). It has 16GB 2RX8 DIMMs. I had asked the vendor to make sure it was the same RAM and he whiffed.)
DELL-Chris H
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May 1st, 2025 12:36
Gestetner,
2rx4 dimms are supported on the R730, as seen on page 84 here. Also, I have multiple 2rx4 dimms listed under the server.
Generally, 2Rx4 DIMMs can offer slightly better performance in certain workloads due to their higher number of DRAM chips, which can lead to better parallelism and bandwidth However, the difference is often minimal and may not be noticeable in all scenarios.
Yet, I think this will boil down to what you prefer and expect.
Let me know if this helps.
Gestetner
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May 1st, 2025 17:54
@DELL-Chris H
Hi Chris. Thank you for replying. I am familiar with that page of the manual. That's actually what I was referring to.
The problem is that the manual only specifies 2RX4 for 32GB DIMMs. There are three listings for 2RX4 in the manual and all three are 32GB DIMMs I don't have 32GB DIMMs and that's not an option for me.
I have 16GB DIMMs. If you look at that section of the Dell manual, every supported configuration using 16GB DIMMs specifies 2RX8. Every listing for 16GB DIMMs specifies 2RX8.
I would assume that Dell engineers had a reason for these specs and that it was not an accident or a mistake. They did list 2RX4 for 32GB DIMMs so I assume it's not a situation where new products came on the market after the manual was drafted.
Can you shed any more light on this? Is there updated product literature with alternate configurations? I really have to imagine there was a reason why or they would have listed it as an alternative.
(edited)
Gestetner
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May 1st, 2025 17:59
I don't know why, but the website is compressing my reply above so there are no spaces between the paragraphs. It comes out as one big jumble. I tried to fix it but it keeps reformatting it for some reason.
DELL-Chris M
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May 1st, 2025 18:17
@Gestetner
Testing. Pre-post appearance screenshot =
* Turn the U2724DE off
* Turn the computer off
* Disconnect all U2724DE cables from the computer
* Disconnect every cable (yes, even power cable) from the U2724DE
* Press and hold in the U2724DE power button for 8 seconds
* Reconnect the power cable and TB4 cable to the U2724DE
* Reconnect the TB4 cable to the computer
* Turn the computer on
* Turn the U2724DE on
DELL-Chris M
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May 1st, 2025 18:18
It kept my formatting?
Gestetner
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May 1st, 2025 18:42
@DELL-Chris M
Your test reply was not squished together and still had spacing and indents so it looks like it kept the formatting. I have no idea why it did it with my reply.
Do you have any more thoughts on my reply today about the manual and DIMM specs?
(Edit. I also see this reply as squished even though it has multiple paragraphs. Oh well.)
(edited)
DELL-Chris M
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May 1st, 2025 18:50
Not sure why your reply messed up. I am using Google Chrome browser. You?
I am in Consumer support and the Forum nuts and bolts guy!
DELL-Chris H is the trusted Enterprise liaison so we should trust his posting above.
Gestetner
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May 1st, 2025 18:57
@DELL-Chris M
All of the above replies and the original post were done on the same computer with Firefox (with various extensions).
This reply is done with Chrome using the same computer.
This is done with three paragraphs, spaced apart. We'll see if it happens again.
(Edit. It now has four paragraphs squished together. Since it's a completely different browser, it must be something on Dell's end.)
(edited)
Gestetner
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May 1st, 2025 19:03
I just noticed that it was two different Chris' posting. I would still like to hear back from
@DELL-Chris H about my reply above noting what the manual specifies (listing 2RX4 only with 32GB DIMMs, and NOT for 16GB DIMMs).
DELL-Chris H
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May 1st, 2025 19:35
Sorry for the delay, I was just researching the issue. While the manual doesn't show it, 16GB 2rx4 dimms are supported on the server and are listed under the supported parts.
DIMM,16G,2133,2RX4,4GDR4,M,Z
I am not certain as to why the manual wasn't amended to include them, but I do see them listed.
Now an issue I do see with the dimms you got is that ALL the 16gb 2rx4 dimms listed for the R730 are listed as 2133Mhz, none are 2400. Now while the server will slow them to 2133mhz, that is the only thing I am seeing.
Also, with the manual showing the 32gb 2rx4 configuration as supported, the 16gb should also be supported as they share the same exact amount of DRAM chips and data organization, and also fall below the supported capacity limitation of the 32gb.
Gestetner
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May 1st, 2025 19:45
@DELL-Chris H Thanks for the follow up. The DIMMs that were sent with the machine were not 2133MHz. They are 2400MHz. Can you clarify your reply regarding the effect of using 16GB 2RX4 2400MHz DIMMs in this machine? Versus using the 16GB 2RX8 2400 MHz that the manual specifies? Are you saying that the machine will slow the latter DIMMs down to 2133MHz?
(edited)
DELL-Chris H
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May 1st, 2025 20:30
I can't be certain to the effect of using the 16gb 2RX4 2400's as there isn't a dimm listed as supported with those specs. I was aware that you had received the 2400Mhz dimms, hence why I was saying the only issue I see on them is that the only 16gb 2RX4 dimms we offer are listed as 2133Mhz, and none of the 16GB 2RX4 dimms we offer are 2400Mhz.
While the server does support mixing of x4 and x8 dimms, as seen on page 81 of the manual I sent, it will slow the faster dimms to match the slower.
So in short, in my opinion, if you have an issue with the dimms they sent, you can always address it as a dimm that Dell doesn't offer for that server, even by specs.