ESXi and VM core count question.

Angry

Limp Gawd
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Feb 27, 2006
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Right now I only have a few VMs setup on a quad core system..the one in my Sig.
If I set both VMs to have 3 cores..does that cause an issue for when both VMs happen to get busy for whatever reason? One is a plex/subsonic server the other hosts random older games.
 

deaedius

Gawd
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highly possible, you could review performance summary and see how things look. Plex isn't very taxing unless serving multiple devices at the same time. I'd guess you'd be just fine.
 

0ptional

Don't Trust Your Friends with Your Decanter
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ESXi will allow you to over-provision the available cores to virtual machines and then handle the load balancing itself. It's generally not the best option, but it works.

Why are you starting by setting them to 3 cores each?

Also this. Why?

3 seems like an odd number to use, plus it's likely you're assigning more CPU power than is actually necessary for the tasks you have going on in those VM's.
 

biggen

Kyle's Personal Blog is Awesome
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Agree with above. Always start with 1 core per VM, monitor, and adjust if needed.
 

Angry

Limp Gawd
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Feb 27, 2006
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I threw "3" out there for each VM because its more than what the box physically has...

Right now I actually have the Plex vm set to three cores and the other VM set to one core. This is my play around box and im only slowly working myself into it. I wasnt sure how ESXi would handle both VM getting busy and not having enough cores, if it would just bog down or divide up the load from each VM as best it could till things settled down. ill try one core on plex and see how she rolls.

On another note..
Im also guessing things like Intel Quicksync dont get used by any of VMs since they are virtualized. (Say if I had an intel cpu I stead of a AMD) I've noticed the AMD Plex VM struggles a bit on blue rays where as my bare metal Plex on the Core i3 2100 doesnt as much.
 

Mackintire

2[H]4U
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I never build a VM with less than 2 cores and rarely provision a VM with more. If the activity level is low enough I'll drop the number of cores. If the VM actually uses more than 80% of its CPU I'll add another core until it doesn't scales or the performance is adequate. There's also a vCPU ratio/ vCPU wait time value to worry about....too many cores without enough idle host cores to service them results in high vCPU wait times, which kills performance. So it's a balancing act. On our deca-core, dual socket boxes, with our workload somewhere around 160 active vCPUs, I start to see vCPU wait times on quad core VMs climb into the 2-5ms wait state time. 10ms is the general (Do not go past this number, threshold)
 

bigdogchris

Fully [H]
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Right now I only have a few VMs setup on a quad core system..the one in my Sig.
If I set both VMs to have 3 cores..does that cause an issue for when both VMs happen to get busy for whatever reason? One is a plex/subsonic server the other hosts random older games.
It can cause latency in the CPU Ready timer which is a measure of the CPU's availability to service request.

A mistake many people make with VM's is treating them like you would a normal server; moar cores = better. That's not true at all. A VM you always start with just 1 core and only increase if there is a need. People can actually hurt performance by adding more cores to their VM's in a multiple VM environment because it's causes a conflicts between core availability.
 
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