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Different amounts of RAM in Hyper-V Hosts RRS feed

  • Question

  • Hi there,

    I have a client with a Windows Server 2016 Hyper-V failover cluster consisting of 2 DL 380's with 1024 GB RAM on each.

    The client is running out of CPU resources and is considering buying a new server (another DL 380) to join to the cluster. Is it necessary to have the same amount of RAM (1024 GB) on the new host or can we install less RAM?

    Will installing less RAM on the additional cause the cluster validation wizard to fail and will this configuration be supported by Microsoft? I cannot seem to find any official guidance.

    Thanks.

    Wednesday, October 2, 2019 8:22 AM

Answers

  • Though it is not recommended, you can have cluster nodes with varying amounts of memory.  It will not cause the validation wizard to fail, but the wizard will report a warning about the different configuration.  Microsoft will support the configuration.

    Some things that you should be aware of.  Generally when configuring memory on the nodes of a cluster with only two or three nodes, the amount of memory configured is configured for the worst possible scenario - all VMs running on a single host.  If the new host does not have enough memory, during a failure situation, you may not have all the VMs available due to lack of resources.  There are ways to plan around this, but it should be noted.

    Secondly, even though you are purchasing another node of the same model as the existing nodes, you may still have to configure the CPUs in your VMs for processor compatibility in order for live migration to work.  I have seen this happen more than once.  It's not a big deal.  In fact, it is often recommended that one configure processor compatibility on VMs running in a cluster.  There are very, very few VMs where such a configuration noticeably impact performance.


    tim

    • Marked as answer by ha20 Wednesday, October 2, 2019 7:59 PM
    Wednesday, October 2, 2019 1:59 PM

All replies

  • Though it is not recommended, you can have cluster nodes with varying amounts of memory.  It will not cause the validation wizard to fail, but the wizard will report a warning about the different configuration.  Microsoft will support the configuration.

    Some things that you should be aware of.  Generally when configuring memory on the nodes of a cluster with only two or three nodes, the amount of memory configured is configured for the worst possible scenario - all VMs running on a single host.  If the new host does not have enough memory, during a failure situation, you may not have all the VMs available due to lack of resources.  There are ways to plan around this, but it should be noted.

    Secondly, even though you are purchasing another node of the same model as the existing nodes, you may still have to configure the CPUs in your VMs for processor compatibility in order for live migration to work.  I have seen this happen more than once.  It's not a big deal.  In fact, it is often recommended that one configure processor compatibility on VMs running in a cluster.  There are very, very few VMs where such a configuration noticeably impact performance.


    tim

    • Marked as answer by ha20 Wednesday, October 2, 2019 7:59 PM
    Wednesday, October 2, 2019 1:59 PM
  • Hi Tim,

    Thanks very much.

    Kind Regards.

    Wednesday, October 2, 2019 9:10 PM
  • Hi,

    I'm glad the information here is helpful to you!

    Thanks for your sharing and support.

    Have a nice day!

    Best regards,

    Michael


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    Thursday, October 3, 2019 5:54 AM
    Moderator