Niren
1 Nickel

T7810 - Mixing RAM Question (2Rx4 and 2Rx8)

Hi All,

I'm hoping to get some advice on adding more RAM to my system. Currently, I have 4 X 16GB (DDR4-2400 2Rx8 ECC RDIMMS) installed. 

I tried upgrading to 8 x 16GB but that didn't work and was told by Dell support that the T7810 doesn't support all 8 slots at 2400 -- I'd have to get new RAM @ 2133 -- which isn't cost effective. I validated that populating 6 slots work getting me to 96GB. 

So, I was thinking of getting 2 X 32GB to add to the system but those only come in 2Rx4 and not 2Rx8. So, the question is if this configuration is supported -- i.e. mixing 4 X 2Rx8 and 2 X 2Rx4 chips.

Thanks in advance for the help.

0 Kudos
5 Replies

Re: T7810 - Mixing RAM Question (2Rx4 and 2Rx8)

• Memory modules of different sizes can be mixed (for example, 2 GB and 4 GB). But, all populated channels must have identical configurations. • Memory modules must be installed beginning with the first socket. NOTE: Registered DIMMS (R-DIMMs) and Load Reduced DIMMS (LR-DIMMs) cannot be mixed. • If memory modules with different speeds are installed, they operate at the speed of the slowest installed memory modules. NOTE: If all DIMMs are 2133, the CPU ordered may run the memory at a slower speed.

T7810 Owner's Manual.pdf

Precision T7810 Spec Sheet

The above is pasted from pg. 34 of the owner's manual.

If using non-Dell memory,.Crucial is highly recommended as it's guaranteed to work in Dell's.  Kingston Value Brand (KVR) almost never works.  Volts can be off in off-brands causing further problems.  Make sure brand name and MHz are still the same.

- Please consider giving posts you like a thumbs up.
- Please "Accept as Solution" posts that are a solution.

I'm a big fan of Dell, a Dell user, and not an employee. This forum is mainly user to user with occasional moderation or additional knowledge by a Rockstar or Dell employee.
0 Kudos
Niren
1 Nickel

Re: T7810 - Mixing RAM Question (2Rx4 and 2Rx8)

Right ... I did see that part in the manual. But this question is a bit more specific Smiley Happy. It isn't an issue of size it is about slightly mismatched specs on the data-bus width especially because how ECC works is different between 2RX4 and 2RX8. I'm just not sure if the motherboard/bios will adapt to it.

0 Kudos
bmcowboy
3 Zinc

Re: T7810 - Mixing RAM Question (2Rx4 and 2Rx8)

Hi @Niren ,

Thank you @bradthetechnut calling me out for this post. Let's break down your questions:


So, I was thinking of getting 2 X 32GB to add to the system

I'm afraid not. Page #53 on the owners manual stated "Memory module capacity: 4 GB, 8 GB, and 16 GB" only.


So, the question is if this configuration is supported -- i.e. mixing 4 X 2Rx8 and 2 X 2Rx4 chips.

Many discussion on this topic as most user guides and manuals emphasis only on matched memory type (e.g. UDIMM, RDIMM, LRDIMM, etc.) or rank (e.g. dual rank, quad rank, etc.) but not data-bus width (e.g. x4, x8, etc.). In fact, it should be fine provided that memories with same data-bus width installed in pairs on the same DIMM channel. Several discussions as listed below for reference. 

It isn't an issue of size it is about slightly mismatched specs on the data-bus width especially because how ECC works is different between 2RX4 and 2RX8. I'm just not sure if the motherboard/bios will adapt to it.

A Dell moderator explained in this thread that "The x4 & x8 refers to the number of banks on the memory component or chip. The higher the number of banks, the fewer the chips in the memory module, the better the reliability and power consumption. Our servers support mixing memory modules of different Ranks and number of banks."

Lastly, if you want to know more about data bus width, you may read on this article.

Hopefully information above helps.

 

“May the Force be with Dell.”
Niren
1 Nickel

Re: T7810 - Mixing RAM Question (2Rx4 and 2Rx8)

Thanks guys in helping out on this issue Smiley Happy This information helps a lot. Just clarifying a couple of things for future folks.

The system does in fact support 32GB chips (page 35 of the manual has additional guidelines that show that information). And, I can confirm that mixing x4 and x8 does work -- as long as the channels are matched.

I went ahead and ordered the RAM (just got delivered) and am currently running the 32GB DDR4-2400 2RX4 in both the DIMM1 slots of CPU 1 and 2 and 16GB DDR4-2400 2RX8 in the DIMM2 and DIMM3 slots of both CPUs. The DIMM4 slots are empty. This gets me 128GB with 6 out of the 8 slots populated.

Let me know if anyone has further questions. 

Again, thanks all for the help -- much appreciated.

Re: T7810 - Mixing RAM Question (2Rx4 and 2Rx8)

You're welcome.  And that's true for pgs. 35 & 53 of the manual.  So it's either a typo or missed info an pg. 53.

- Please consider giving posts you like a thumbs up.
- Please "Accept as Solution" posts that are a solution.

I'm a big fan of Dell, a Dell user, and not an employee. This forum is mainly user to user with occasional moderation or additional knowledge by a Rockstar or Dell employee.
0 Kudos