Proper DL380 G6/G7 DDR3 memory configuration for vSphere

[Brian Proteau]

Below this sentence is the gist of my question. If you want more information, you can look at the details in the chart labeled "DIMM slot/capacity/populated speed table " in the HP DL380 G7 quick specs here http://h18004.www1.hp.com/products/quickspecs/13595_na/13595_na.html#Memory

I am thinking of adding additional memory to each ESX Host. The resulting DIMM configuration will bring me to 3 DIMM Per channel essentially lowering my max DIMM speed from 1333MHz to 800 MHz.

I understand there are other factors to consider and channels may be more important but haven't found anything speaking specicially to vSphere or even virtualization in general. I have to believe one is a better choice. Bottom line is I don't want to drastically or even slightly noticeably affect performance with the proposed configuration change.

I have read through this but, still haven't found anything to push me definatively one way or the other.

http://dl.dropbox.com/u/9715225/DDR3%20Configuration%20Recommendations.pdf

Current:
2-DIMM per channel(12-8GB DIMMs)
1333 MHz
96GB

Proposed:
3-DIMM per channel(18-8GB DIMMs)
effectively 800MHz
144GB

[Michal Kapalka (mikap) · Accepted solution]

hi,

check this sites about the memmory :

http://h18004.www1.hp.com/products/servers/options/memory-description.html

http://h18004.www1.hp.com/products/servers/options/tool/hp_memtool.html

In my personal opinion the G6 and the G7 options of the memmory is the same.

mikap

[Brian Proteau]

Yes. G6/G7 memory is the same and I have seen those links but, the tool just tells you best configuration for a specific amount of memory.

My question is more about DIMM speed and memory channels as they relate to total performance in this case for a vSphere ESX server.

When incresing channels from 2-3, DIMM speed decreases. I'd like to find performance comparisons between my 2 scenerios. Does adding a channel (from 2-3) but lowering DIMM speed (1333-800 Mhz)increase or decrease observed performance?

[Michal Kapalka (mikap)]

hi,

of course the performance will be decreased if add more memory modules per channel, you will decrease the frequency MHz. It always depend on the application running inside the VM.

mikap

[Daniel Bowers]

The answer will always be "it depends", but it comes down to whether your current 96GB configuration is memory constrained. (And if it is, whether it's constrained on capacity or bandwidth.)

My $0.02: Check the host memory utilization metrics under VMWare, especially Swap Used and Memory Balloon graphs. If either of those two are high, you're probably memory constrained, and you might be better off with 144GB. If both are relatively low, stick with 96GB.

[Brian Proteau]

We use an N+1 philosophy so we rarely share much memory and are never constrained. The question is if you have 2-DL380 G7 ESX Hosts identical except for the memory configuration outlined, whhich would "generally" perform better without constraints.

I do assume there are alot of "it depends" related to VM roles etc. but, I would guess that the performance scale would tip one way or the other using a broad spectrum of applications.

I'll probably do these tests myself but, wondered if their was any data out there or what peoples theories might be.