R715 Memory Configuration Not Optimal - After Upgrade

Hello.

Your memory configuration is not optimal because the memory channels are not balanced thus; slots on each channel must have identical memory modules for both processors. For optimal memory, you will have:

A1, A2, B1 &B2 =16 GB

A5, A6, B5, &B6 = 8 GB

The rest of the slots ought to remain empty.This will give you total memory capacity of 96 GB. However, if want more than 96 GB of memory and are looking to use 16 GB DIMMs, consider purchasing 4 additional modules(16 GB) to be populated on the remaining slots in the similar manner.

I tried the memory in the listed solution of :

A1, A2, B1 &B2 =16 GB

A5, A6, B5, &B6 = 8 GB

and still received the "Memory not optimal" error.  Thinking that it could be an issue with 2 different speeds of memory, I tried only installing the 16GB modules as:

A1, A2, B1, B2 and still received the "Memory not optimal" error.

Thanks again.  I greatly appreciate the assistance!

Thanks for the info Robert!  I will try to see if that configuration works.

Where can I find more information about the "Channels" of memory as they relate to my Dell server.  I have more experience with HP (boooo) and find it more difficult to understand the Dell layout.

Mixing memory with different speed means the channels will operate at the fast frequency. Ensure that you set the memory mode to Memory Optimized. Again, for optimal memory configuration, the memory channels must have identical DIMMs hence balanced. You will therefore need additional 4 8GB DIMMs (total of 8 8GB modules) to populate on the rest of the slots i.e A5, A6, A7 &A8 and B5, B6,B7 &B8. Populating  only slots A5 &A6 on CPU 1 and B5 &B6 on CPU 2 creates memory imbalance with channels C&D on CPU 1 and CPU 2. Memory in the channels have to match. See diagrammatic illustration below:

Thanks for the info Robert,

I'm a little confused, you stated that A1, A2, B1 &B2 =16 GB & A5, A6, B5, &B6 = 8 GB would provide optimal memory configuration, but when I installed it in this configuration it was not optimal.

Also, it was my understanding that the mixed memory speeds would operate at the slowest common frequency, not the fastest frequency.

With the configuration of  A1, A2, B1 &B2 =16 GB & A5, A6, B5, &B6 = 8 GB the DIMMS would create an imbalance across channels C&D correct?

In your latest post, you stated that memory channels must have identical DIMMS in each channel,  does that mean that Channel A,B,C,D must be populated or can channel A,B be populated only?

Robert,

Thanks for the update.

I am currently on BIOS 1.5.2

I did attempt to only populate A1, A2, B1 &B2 with 16GB DIMM, I still received the "Memory not optimal error"

Pardon me, the channels will operate at slower speed when memory with different speeds are mixed. With the configuration of  A1, A2, B1 &B2 =16 GB & A5, A6, B5, &B6 = 8 GB, there won't an imbalance across channels C&D because they are empty. Imbalance occurs when memory on channels C&D does not match memory on A&B. Yes, can populate only A&B channels. Some BIOS versions do not support 16 GB memory modules. What is your current BIOS?

The BIOS is way out of date. Apply the following BIOS updates first then followed by respective iDRAC updates.

BIOS    iDRAC

BIOS    iDRAC

BIOS    iDRAC

BIOS

Thanks for the info Robert.  Do you know if I can accomplish the same updates by using the Dell  Deployment Toolkit CD?

Sure: <ADMIN NOTE: Broken link has been removed from this post by Dell>. See instructions at the bottom of the page. Mean while, you may also perform updates via the LifeCycle Controller (LCC) using F10 during POST. Got to Platform Updates and point to ftp.dell.com site.

Thanks Robert, I will check that out.

I was looking at downloads.dell.com/.../poweredge-r715_reference%20guide3_zh-cn.pdf

And the common theme that I see is that in almost all configurations, A1,A2,A3,A4 B1,B2,B3,B4 are always fully populated.  I do not see the configuration that you suggested of  A1, A2, B1 &B2 =16 GB & A5, A6, B5, &B6 = 8 GB listed

You are perfectly right. However, there can be different configurations depending on the number of available memory modules and whether they are of the same capacity or mixed capacity. Now if we are looking to populate all channels as per the guide, try adding 4 more 16 GB modules as previously suggested. Have you already updated the BIOS?

Robert,

I upgraded the BIOS, Lifecycle Controller, iDRAC and tried the following configuration of memory:

A1,A2, B1,B2 X 16GB

and still received the not optimal error.  To ensure that the issue was not related to the 16GB DIMMS, I installed the 8GB DIMMS in the following :

A1,A2, B1,B2 X 8GB

I still received the not optimal error.

I noticed the first time that I booted into the (non updated version) Lifecycle controller, Error messages (these before I had made any changes to the memory configuration) *Please see attached Photo*

After the updates were performed, I did not notice this error when I entered the Life cycle Controller.

I installed the following configuration:

A1,A2,A3,A4 B1,B2,B3,B4 - 8GB

added

A5,A6,A7,A8 B5,B6,B7,B8 - 4GB DIMMs

System was satisfied with the memory.  Is it possible that the documentation is incorrect and all channels must be populated?  

Hello.

I have looked at a couple of documentations including the R715 source book. However, I haven't found this requirement. Allow me to consult then I will post my findings.