ESXi

We are refreshing several Dell R620 ESXi hosts - looking at the R630 CPU options its constraints type problem: what is the optimal clockspeed (GHz), cores/socket, memory speed, cache/price?

We are much more memory constrained that CPU constrained according to our current vCenter stats, (we have an average 20:1 VM:host ratio) and CPU are mostly idle while memory is often showing much higher in our clusters, especially during host maintenance and upgrades.

With that in mind, we are leaning towards higher GHz (run fewer threads faster) strategy with the Intel® Xeon® E5-2643 v3 3.4GHz,20M Cache,9.60GT/s QPI,Turbo,HT,6C/12T (135W) Max Mem 2133MHz option.

Thereby, saving money on the CPUs to max out the memory (vCenter shows our clusters are CPU idle and more memory constrained).

Interested in hearing how others make the same type of HW refresh decisions in terms of CPU:memory:cost, etc (see attached CPU options)

thanks for any constructive feedback/tips!

Hi there,

if your consolidation ratio is this high I wouldn't recommend you going down on CPU core count by much - if the overprovisioning ratio reaches certain threshold you will get killer CPU Ready values which will significantly slow down your VMs. If you could do an investigation of your VMS' CPU Ready stats and check if they are well below 5% at their peak usage times - Ideally up to 2% if you want to decrease CPU Cores - that'd be great.

Since VMkernel needs the whole physical CPU core available while processing a VM's vCPU cycle (1:1 ratio), you could end up with contention. I'd suggest using the same number of cores but with lower frequency if available - HyperThreading can help you with 5-10% additional overhead while running the VMs.