Description

You can set the proportion of CPU resources that can be reserved for each node in the cluster between 30% and 80%, and the default is 80%. If CPU reservation is enabled for a VM, it can preempt resources to ensure performance when needed, and the idle CPU resources can also be used by other VMs. Compared to the CPU exclusive mode, CPU reservation has a higher resource utilization. Total vCPU Cores Reserved = Number of Physical CPU Cores * CPU Reservation Ratio.

VMs with CPU reservation enabled will preferentially get CPU resources when they need them, effectively enhancing their performance during periods of high load. However idle CPU resources of these VMs can also be used by other VMs. 80% of node CPU cores are reserved by default, which can be modified in System > Cluster Settings > CPU Reservation Ratio Settings.

Precautions

When the proportion of CPU resources used by VMs on a node reaches the CPU reservation ratio set for the node, you cannot start another VM with CPU reservation enabled on the node.

Enabling CPU reservation for too many nodes with hyper threading enabled and high load will reduce the CPU usage displayed on the page, because the resource preemption of CPU reservation is calculated based on the number of physical CPU cores, while the CPU usage is calculated based on hyper threading.

Enabling CPU reservation will make the High Priority option checked and the following options unchecked: Memory reclaiming, Enable CPU exclusive mode, and Set CPU clock speed to. If CPU reservation is disabled, the options mentioned above will not be modified. You can modify them manually.

Prerequisites

None.

Steps

 Go to System > Cluster Settings > CPU Reservation Ratio Settings to configure the Global CPU Reservation Ratio and CPU Reservation Ratio for each node.

Select Enable CPU reservation and specify schedules for enabling CPU reservation when creating and editing a VM, and click OK.