Hyper-V over or under allocating vCPU's RRS feed

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  • 1. This forum isn't the best one for Hyper-V, you'll get more responses when asking about Hyper-V here:

    This forum is for Virtual Server 2005.

    2. The technet article is lot and is out dated.  The 8 vCPU per core isn't used as a metric any longer, and you can assign more than 4 vCPUs with newer versions of Hyper-V.

    3. Don't "evenly spread" your cores out.  You use the number required.  Start at 1 or 2, then go up.  Adding too many will hurt performance, not help it.  You don't want to over allocate your resources.  VMs don't work like physical machines in this respect.  A DC with a low number of users can easily run on 1 vCPU

    4. Don't think in "cores."  You're basically assigned a VM a percentage of CPU usage.  The more vCPUs, the higher the percentage, but what you'll also see is that if you have 6 vCPUs assigned, the host needs to get all that extra processing power free at one time which can degrade performance.

    5. There's no problem with having unassigned CPU/cores in Hyper-V.   Left-over CPU is fine and is common with the multicore processors now.  Disk I/O and RAM are often the first to performance issues in virtualization.

    tl:dr -- assign what you need (and nothing more) to prevent your VMs from running at 100% CPU usage, or having big usage spikes. 

    Thursday, December 21, 2017 5:00 PM