Fastest server ram configuration for 48GB?

Question

I have an HP ProLiant DL160G6 server, with 2 CPU's and 48GB ram, with following modules:

4x 8GB Module - DDR3 1066MHz (KTH-PL310Q8/8G)
4x 4GB Module - DDR3 1333MHz (KTH-PL3138/4G)

I'm re-purposing the server now to be a VMWare host, and wonder what would be the fastest RAM configuration placement?

Also, will it make any sense to place faster memory (16 GB on 1333MHz) on 1st CPU, and slower on 2nd, despite it creating an non-even configuration (16 + 32)?

Otherwise, should I just place:

P1 - Channel 0 - 2x 8GB
P1 - Channel 1 - 2x 4GB
P2 - Channel 0 - 2x 8GB
P2 - Channel 1 - 2x 4GB

Are you sure it matters? Because traditionally RAM SPEED is not exactly a distinguishing factor for a virtualization host. THey normally are in this order: Disc IO, RAM Amount, CPU speed. As long as CPU speed is not a limiting factor (and interesting enuogh that is where the ram speed comes into play as it makes the CPU faster) it is a total non issue. — TomTom, Feb 04 '14 at 11:29
You have a point, though I do would like to get the best performance I can. — SyRenity, Feb 04 '14 at 11:33
Since you *can* put the same amount of RAM on each channel (12 GB), and perfectly balance both your CPUs and channels, why would you possibly not want to do that? — David Schwartz, Feb 04 '14 at 13:23
After studying the subject deeper, it's indeed seems to be the only way. — SyRenity, Feb 04 '14 at 16:37

score 11 · Accepted Answer · edited Apr 13 '17 at 12:14

For an HP ProLiant DL160 G6, there are a few things to consider.

First, that's not HP RAM!!! It's Kingston Memory. Furthermore, your 8GB module is a Quad-Rank DIMM and the 4GB module is a Dual-Rank DIMM. (Here's why ranks matter) This complicates things, as HP does not sell a Quad-Rank 8GB module in the product lineup.
Second, you must upgrade the firmware of your system (here's why), either via the individual firmware updates or via the HP Service Pack for ProLiant DVD. There were BIOS changes that impacted memory for that model.
Third, the most optimal configurations can be found via the HP Memory Configurator Tool. What you have in terms of parts is not ideal. At this point you just need to follow the Nehalem/Westmere DIMM population guidelines.

Summary:

Balance the DIMMs across CPUs.
Heaviest rank goes farthest from the CPU in each bank.
The presence of Quad-Rank memory will limit you to only using 12 of the 18 slots in the server.

So, your best option is for each CPU, populate Slots A and B with 8GB modules. Populate Slots C and D with 4GB modules.

The result will likely run at 800MHz instead of the native 1066MHz of the 8GB sticks or the 1333MHz of the 4GB sticks. If you remove two of the 4GB modules, the system will probably run at 1066MHz.

Thanks for the very detailed answer! I'm always confused with the correct placement of RAM modules, and glad there are some experts here who already cut their teeth at this. Is there any way to see what the exact speed will be, so I could decide if I should put all 48 GB, or just 32? — SyRenity, Feb 04 '14 at 15:46
Reading here, it seems that the difference in speed is actually very negligible: https://communities.vmware.com/thread/306073 — SyRenity, Feb 04 '14 at 16:19
Also just to confirm, any sense taking NUMA into account here, or the different RAM size will not allow it? — SyRenity, Feb 04 '14 at 16:22
I'm just trying to tell you how to arrange the RAM in the server. You really don't have any other options. — ewwhite, Feb 04 '14 at 16:23

Fastest server ram configuration for 48GB?

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