VMware vSphere

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  • 1.  Possibility to reserve CPU cores to VMs?

    Posted Jun 12, 2025 06:37 AM

    Hello, 

    we are running vSphere 7 (soon to be upgraded to 8) running on 8 ESX servers.

    We are requested to prepare several VMs for a software from a third party vendor. This software vendor wants us to "reserve vCPU and RAM" specifically for the servers used for their systems. The total amount of vCPUs their VMs use is 52 (which is a lot considering that we have a total of less than 200 vCPUs in our VMWare environment...)

    I could not find an option to reserve a number of vCPUs to single VMs, is this even possible? I could use CPU reservation based on GHz but from the documents they have sent me the reservation should take place based on vCPUs.

    From my (limited) understanding of vSphere i guess i could raise the CPU shares of this VMs to give them precedence over other systems but still i guess this is not a "real" reservation of vCPUs.

    Can you tell me how to reserve vCPUs for the VMs?



  • 2.  RE: Possibility to reserve CPU cores to VMs?
    Best Answer

    Broadcom Employee
    Posted Jun 12, 2025 06:39 AM

    You cannot reserve a vCPU, you reserve an X number of MHz/GHz. What kind of software is it? I would typically not recommend setting a reservation for such a high number of total vCPUs to be honest. It just makes life (DRS and HA) more challenging and is fairly costly, as a reservation means no one else can use those resources.




  • 3.  RE: Possibility to reserve CPU cores to VMs?

    Posted Jun 12, 2025 07:43 AM

    Hello Duncan,

    thank you very much for your answer. Its a so called "PACS" used in the medical field for handling of x-ray images. For sure it requires a lot of resources but as our whole environment has only a total number of less than 200 vCPUs we would really struggle to reserve about 25 % of our CPU resources for one single system. 

    Up on this i could not find a way how to set it up technically , but as you explained its not possible anyway (only indirectly via GHz reserveration).

    Thank you very much and kind regards


    Original Message


  • 4.  RE: Possibility to reserve CPU cores to VMs?

    Broadcom Employee
    Posted Jun 12, 2025 07:46 AM

    yes with PACS I've seen/heard about this requirement before. but considering it is not extremely latency sensitive, personally I would test it to see if it works as expected without.


    Original Message