You can fine-tune the parameters of virtual machines (VM). This will allow you to adjust the performance of the cluster and improve network security. The parameters available for fine-tuning depend on the type of virtualization in the cluster.

Changing the fine settings is not recommended if you are not completely sure about your actions.

Available parameters

Clusters with KVM virtualization

  • resources:
    • vCPU — CPU count;
    • RAM — RAM, MB;

    • Storage — main disk space, GB; 

      For the platform to be able to resize a disk, the storage must have free space of at least the same size as the original disk.

    • partition for extension — the partition of the main disk that will be enlarged when the Storage parameter is changed. For example, /dev/sda2 or sda2;

      1. You can specify an external or an internal partition name. For example, the /dev/sda2 section in CentOS 8 can have the internal name /dev/vda2. Specify the internal name only if this partition is mounted on the system.
      2. To enlarge the disk by creating a new partition, leave the parameter blank. VMmanager will add unallocated disk space to the VM. You will be able to create a new partition in this space using the OS.


  • limits:
    • CPU weight — CPU usage priority. Values range from 128 to 10000. For example, a VM weighing 2048 will access the CPU twice as often as a VM weighing 1024;
    • I/O usage weight — input/output operations priority. Values range from 100 to 1000. For example, a VM with the I/O weight of 200 will perform read and write operations to disk twice as often as a VM with the weight of 100;
    • read speed, IOPS;
    • write speed, IOPS;
    • read speed, Mbps;
    • write speed, Mbps;
    • inbound traffic speed, Mbps;

    • outgoing traffic speed, Mbps;

      VMs with a traffic speed higher than 1000 Mbps may not work correctly.

    • incoming TCP-connections;
    • outgoing TCP-connections;
  • antispoofing settings:
    • Antispoofing enable/Antispoofing disable switch — enable or disable protection against network attacks using the IP-spoofing method;
    • Tagged traffic is permitted/Tagged traffic is not permitted switch — allow or deny traffic with the VLAN tags;

  • port restrictions — restriction of connections to certain virtual machine (VM) ports. Read more in Restricting access to a VM;

  • VM disks settings:
    • Storage — disk space, GB;

    • partition for extension — t he partition of the disk that will be enlarged when the Storage parameter is changed. For example, /dev/sda2 or sda2;

  • virtualization parameters:
    • CPU emulation mode — VM CPU specification defining method :
      • By default — QEMU virtual CPU is emulated;
      • Host-model — the emulated CPU will have the same function flags as the cluster node CPU;
      • Host-passthrough — the emulated CPU will exactly match the CPU on the host machine cluster node and have the same function flags. This emulation mode provides better performance and may also be mandatory for some applications. Migration of such virtual machine is possible only to the fully matching CPU.
    • boot loader type — BIOS or UEFI.

Clusters with LXD virtualization

  • resources:
    • vCPU — CPU count;
    • RAM — RAM, MB;

    • Storage — disk space, GB;

      For the platform to be able to resize a disk, the storage must have free space of at least the same size as the original disk.

  • limits:
    • CPU weight — CPU usage priority. Values range from 0 to 10. For example, a VM weighing 2 will access the CPU twice as often as a VM weighing 1;
    • I/O usage weight — input/output operations priority. Values range from 0 to 10. For example, a VM with the I/O weight of 10 will perform read and write operations to disk twice as often as a VM with the weight of 5;
    • network weight — priority in time allocated for processing requests . Values range from 1 to 10. For example, VM requests with a network weight of 2 will be allocated twice as often as VM requests with the weight of 1;
    • process count;
    • read speed, IOPS;
    • write speed, IOPS;
    • read speed, Mbps;

    • write speed, Mbps;

      In the LXD cluster, the following settings cannot be used simultaneously:

      • "read speed, IOPS" and "read speed, Mbps";
      • "write speed, IOPS" and "write speed, Mbps".


    • inbound traffic speed, Mbps;

    • outgoing traffic speed, Mbps;

      VMs with a traffic speed higher than 1000 Mbps may not work correctly.


    • incoming TCP-connections;
    • outgoing TCP-connections;
  • antispoofing settings:
    • Antispoofing enable/Antispoofing disable switch — enable or disable protection against network attacks using the IP-spoofing method;
    • Tagged traffic is permitted/Tagged traffic is not permitted switch — allow or deny traffic with the VLAN tags;
  • port restrictions — restriction of connections to certain virtual machine (VM) ports. Read more in Restricting access to a VM;

  • сontainerization parameters:

    • nested containerization — creating containers inside a container using Docker, Podman, LXC, etc.

Changing vCPU and RAM

The platform allows you to increase vCPU and RAM values without rebooting the VM:

  • vCPU — no limitations;

  • RAM — only in 1024 MB increments and not more than 16 times for each VM.

If the vCPU and RAM values decrease, the VM will be rebooted.

To increase the resource value without rebooting, enable the Add resources without restarting the VM option on the Resources and limits tab.

Fine-tuning procedure

To fine-tune the parameters:

  1. Enter Virtual machines → select the VM → Parameters button → Fine-tuning settings section.
  2. Specify the required parameter values on the Resources and limits tab.

  3. If the VM requires adding resources without rebooting, enable the Add resources without restarting the VM option. 

    To apply this setting, the VM will be rebooted.

  4. Configure Port restrictions for the VM Read more in Restricting access to a VM .

  5. If there are multiple disks connected to the VM in a KVM cluster, specify the required parameter values on the VM disk settings tab. Read more about virtual disks in Managing VM disks. 

    If disk settings are changed, the VM will be rebooted.


  6. Select the required parameter values on the Virtualization parameters (Containerization) tab. 

    If the CPU emulation mode or boot loader type is changed, the VM will be rebooted.


  7. Press Edit (Change and restart).

Performance benchmarks of VMs using third-party software do not guarantee unbiased data. This is due to the limitations of virtualization — the presence of additional levels of abstraction between software and hardware.

An example of resources and limits configuration



Example of VM disks configuration


An example of virtualization parameters configuration

Useful tips

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