I'm having some slight confusion assigning virtual processors to a VM in Hyper-V, possibly due to outdated information on the internet. We have decided to virtualise our servers due to bringing in some new software that requires it's own server, it made more sense to virtualise everything instead of having boxes all over the place.

Our new server is a DL380 Gen9 with an XEON e5-2609v3, it has 6 cores, which is the amount of virtual processors I have in Hyper-V Manager.. in that case i'm assuming assigning 2 cores will essential think it has a dual-core processor?

The system requirements for the software is a dual core cpu, so i'd need to assign 2 as a minimum?

Is it still correct that Microsoft recommends 1-1 assignment of virtual processors to actual cores? so with 6 cores i could create 5 VMs (reserving 1 core for the host). If this is still relevant, it confuses me because i was under the impression this server is capable of handling a lot more.

I can only assume this information is incorrect because 1-1 assignment would mean 1 core per VM which would be quite bad for things like domain controllers or database servers.

I would appreciate some clarification on this issue.


1-1 was NEVER relevant. I would say 99% of the installs have a lot more virtual cores in various machines than physical cores - as long as the machines do not NEED the cores (most of the time) that works markedly well.

1-1 assignments only makes sense in VERY special cases (like a VM using up all CPU doing calculations) and is not a standard case at all.

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  • Thanks for clearing it up, as I suspected a lot of the information online is outdated or incorrect, funnily enough I did see 1-1 mentioned a few times and it completely confused me as I realistically knew the server could handle a lot more. – Goodbytes Jan 15 '15 at 12:23
  • It mostly is idiocy or a side effect (for example: memory or disc IO are so limited that making more virtual cores simply makes no sense - CPU, for most servers, is NOT the limiting factor. – TomTom Jan 15 '15 at 12:35

1-1 doesn't make sense at all. Because the overall aim of virtualization is to use the server resources more efficiently and to have a number of virtual servers within a physical server. In our infrastructure a single physical host has just 4 cores, but we do maintain quite a good number of virtual servers. So, no need to worry about that.

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