Which of the following methods could be used to improve performance and reduce CPU contention of this VM while

It appears that a virtual machine (VM) in a DRS Cluster is having performance problems because it does not have enough CPU resources available. Which of the following methods could be used to improve performance and reduce CPU contention of this VM while maintaining compatibility with DRS (Choose Two)?

A.
set the CPU reservation for this VM to the Average CPU Utilization and the CPU limit for this VM to Peak CPU Utilization

B.
set the CPU reservation for this VM to 100%

C.
increase CPU shares for this VM to High

D.
set CPU affinity on the VM

Explanation:
Assume the VMs CPU usage on the host looks like this currently Assume the cluster has 4000 GHz total CPU available, and that currently the VM has 1000 MHz reserved to it, and peaks at 2000 MHz.
The values Low, Normal, High, and Custom are compared to the sum of all shares of all virtual machines on the server. Therefore if you increase CPU shares for this VM to High, it will gain proportionally more resources, improve performance and reduce CPU contention. Therefore A is correct.
If you set the CPU reservation for this VM to the Average CPU Utilization, (which will be a value between 1000 MHz and 2000 MHz) and the CPU limit for this VM to Peak CPU Utilization 2000 MHz. This will cause the VM to gain additional resources, and should improve performance.
Therefore B is correct.
Affinity rules
In general, don’t specify affinity rules unless you have specific reasons to do so. This will give DRS the maximum flexibility to consider all options for resource management and hence enable the most efficient resource placement. Setting CPU affinity will not increase available resources.
Therefore D is incorrect.
Resource Management and DRS Best Practices
The following guidelines can help you achieve optimal performance for your virtual machines:
When specifying the reservations for virtual machines, always leave some headroom; do not commit all resources. As you move closer to fully reserving all capacity in the system, it becomes increasingly difficult to make changes to reservations and to the resource pool hierarchy without violating admission control. In a DRS-enabled cluster, reservations that fully commit the capacity of the cluster or of individual hosts in the cluster can prevent DRS from migrating virtual machines between hosts. Therefore B is incorrect.

One Comment on “Which of the following methods could be used to improve performance and reduce CPU contention of this VM while

  1. delesc says:

    I read the question differently

    Assume the VMs CPU usage on the host looks like this.
    The cluster has 4000 GHz total CPU available, and that the average that the VM uses is 1000 MHz, and peaks at 2000 MHz.
    If you set the CPU reservation for the VM to the Average CPU Utilization(1000Mhz), nothing will improve.
    Also if you set the CPU limit for this VM to Peak CPU Utilization(2000 MHz). It will still struggles to get that 2000Mhz as there is contention. So no improvement.

    By setting the reserved value to 100% of the CPU allocation, say 2000Mhx it is guaranteed to have more memory.
    So I think B is correct.

    Additionally, using a share value of ‘High’ will increase CPU shares for this VM, so it will gain proportionally more resources, improving performance. Therefore C is correct.

    B & C are correct.


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