LRDIMM vs RDIMM

[TLN]

Hi all.

I'm reading about LRDIMM memory now and advantages of it.
I know it have extra chip which takes care of load, and represents 4 rsnk memory as 2 rank to CPU. I also know that it's more advanced technology then RDIMM, that's cool. And that if I want more then 768Gb of memory - I can only use LRDIMM. 768Gigs is fine, thanks

Say, if I'm ok with all the hard limitations of RDIMM memory (yeah, 768Gig), does it make sense to go for LRDIMM?

I've came into article here: DDR4 RDIMM and LRDIMM Performance Comparison
It shows better performance of LRDIMM, but:

When Registered DIMMs (RDIMMs) are Best
Many of our HPC customers are looking for high speed and low latency. In that realm, RDIMMs are the hands down winner. At slightly cheaper cost and with the ability to ramp up memory frequency on certain motherboards, they are the right choice for fast memory performance.

When Load-Reduced DIMMs (LRDIMMs) are Best
When very large quantities of RAM are the goal, then LRDIMMs are the way to go. In this chart from Intel’s Grantly Platform Memory Configuration Guide, you can see that when packing a system full of RAM you can achieve twice the capacity from LRDIMMs. However, 64GB DDR4 LRDIMMs are still quite costly. There are also specific configurations using 3 DIMMs per channel that require LRDIMMs. Contact one of our experts to discuss the best options when you are considering servers with more than 512GB memory.

Does it mean that LRDIMM are faster or have better latency then RDIMM?
Or if case I have a same price for both - I should pick up LRDIMM as it's more advanced memory?

Thanks.

 

[T_Minus]

There's a very in-depth thread about memory, latency, and comparing LR to regular R as well as DDR3 vs DDR4.
I made the post with references to # of outside sources that go into it a lot, sorry I don't have the link maybe someone else will have it fresh or you can search the forums here.

 

[Evan]

Best to use RDIMM if you can get the required capacity with it, LRDIMM only if you need bigger configuration of memory.

DDR3 16gb and over was usually lrdimm
DDR4 64gb and over is lrdimm generally.

LRDIMM and the fact your usually populating all slots generally means it's slower.

 

[T_Minus]

Really wish I had the old thread with references / more in-depth info...
I think populating all slots RDIMM vs LRDIMM I think LRDIMM is actually faster, but again I don't recall it's one of the things covered in tests in one of the resources I linked too...

OK!!

Gotta find it ha

 

[TLN]

Best to use RDIMM if you can get the required capacity with it, LRDIMM only if you need bigger configuration of memory.
DDR3 16gb and over was usually lrdimm
DDR4 64gb and over is lrdimm generally.
LRDIMM and the fact your usually populating all slots generally means it's slower.

Really wish I had the old thread with references / more in-depth info...
I think populating all slots RDIMM vs LRDIMM I think LRDIMM is actually faster, but again I don't recall it's one of the things covered in tests in one of the resources I linked too...

This is interesting.
I know that LRDIMMS are used when you want to maximize your memory. And that once you populated all the slots - it will work at lower speed. (2133 vs 2400 or 1866 vs 2133). But if I don't populate all the slots, and it work at the same speed - how is performance?
Article (link in #1 post) says that LRDIMM gives better throughput. I cannot get how it can give worse latency with all that.

 

[mstone]

Article (link in #1 post) says that LRDIMM gives better throughput.

Where? Everything I see in that article shows the exact opposite. The only case where LRDIMM would give better throughput would be a configuration where 1 LRDIMM could replace 2 RDIMMs.

 

[TLN]

Oh! That's a good catch!

Strange that testers did 1 Channel and 2 Channel tests, but decide to put 1Channel vs 2 Channel in final table. Now it's getting clear

 

[T_Minus]

I was under impression that if max DIMMS were say 24x that 24x LRDIMM would be > than 24x RDIMM.

It's be a long long time since i've looked at this so maybe I'm wrong.