CPU Cores

[doubleH]

Hello,

I currently have 5 HP DL385 G7 rack mount servers running vSphere 5.1. Each host has 2 12-core AMD Opteron 6100 series CPU's for a total of 24 cores/server.

I have a server refresh coming up and am seriously looking at blades instead of rack mounts. I will also be moving back to Intel CPU's.

I am struggling with how many cores to spec out in the new blades. With my contract pricing with HP I can obtain heavily discounted pricing on 4 cores cpu's and 8 cores are quite a bit more. My reseller is telling me to go with 8-core, but they are not basing that recommendation on any facts which makes me very uneasy.

Does anyone have any recommendations on any tools I can use that would help tell me how many cores I require with the new environment? I have access to VCOPS, but haven't really found anything that would help me.

Thanks

[JeB201110141]

Dear doubleH

What you asking for isn’t an exact science, but I will try to guide you with our own local discussions in mind.

I can’t figure if you go up or down in memory.

If you select 4 cores going from 2*12 cores (who probably in fact is 2*(6*2) cores) you may have to fight more against oversized VM’s with higher number of cores and/or very high CPU usage, against a 8 core. That is all about CPU Contention and CPU/RAM ratio.

In vCOPS you can find vCPU:CPU Ration and vMEM:Physical Memory who can tell how your current usage are in VM’s vs physical.

In my opinion it’s always the memory that is used first, but it would be a disaster if it is CPU who starves.

I would recommend looking in your cluster CPU usage versus RAM usage, before selecting.

-CPU - vCOPS -> select the cluster -> Operations -> CPU Usage -> Workload (%) + CPU Contention (%)

Workload (%) tells your current usage and CPU Contention (%) tells how it handles the load.

Low CPU Contention (%) (under 3-5%) tells you don’t have CPU usage issues in general and your Workload (%) is usable and reliable (here starts the religion ?)

-MEM - vCOPS -> select the cluster -> Operations -> Memory | Usage (%)

How much memory is used against physical over time, over ~90-95% ballooning (and worse) is kicking in, and the trouble may start.

All this sends me back to your question – how many cores pr. blade.

-If you are keeping your current memory size (and the usage is how you like it), and you are going to keep the same amount of VM’s on each hosts,  I would look at current CPU Usagewith with some scenarios, if the CPU Contention is low.

: very low CPU Usage like 5-10% - 2*4 cores would probably not be any trouble.

: some CPU usage like 20-40% - 2*4 cores could have trouble pulling it

: medium usage like 40-60% - 2*4 cores would probably have trouble

My suggestions is from the following - and remember it is just Indicative ! :

G7 AMD is around 3-5 generations older then the newest current CPU’s. A quick look at performance it would yell 2 times better efficiencies.

PassMark - AMD Opteron 6174 - Price performance comparison

PassMark - Intel Xeon E5-2650 v2 @ 2.60GHz - Price performance comparison

2*12 cores vs 2*4 cores is 3 to 1 cores

100% CPU utilization (in 2*12 cores) * 2 eff. * 1/3 cores = 67 % with 2*4 cores.

2*12 cores vs 2*8 cores is 3 to 2 cores

100% CPU utilization (in 2*12 cores) * 2 eff. * 2/3 cores = 132 % with 2*8 cores.

In the end it all comes to prices, and I would go for 8 cores vs 4 cores every time, just because its just a little pricestep from a lot of trouble, and a little pricestep for the hole hardware price.

If the question is about Oracle or other license related cores/license selections, there could be large pricesteps for every core, just to keep in mind.

Hope this helps and show you how awesome vCOPS for everyone

Kind regards

Jesper Baunbæk