This article contains definitions of the key terms used in the VMmanager documentation.

Virtual machines

A virtual machine (VM) is a software system that emulates the operation of a physical server. Several VMs can run on a single physical server. Each VM runs in an isolated environment and does not affect the other VMs. The platform uses QEMU-KVM and LXD hypervisor software to create and manage VMs.

The hypervisor allocates virtual CPUs (vCPUs) to VMs. A virtual processor is a software virtualization of a physical processor. The more vCPUs allocated to a VM, the more physical CPU time it gets. The number of vCPUs determines the number of threads for applications running on the VM.

Learn more about managing VMs in the Virtual machines section.

Clusters and nodes

A cluster is a group of servers where VMs are created and run. Usually the infrastructure administrator combines servers into a cluster based on some common characteristics: e.g. location, amount of resources, configuration of created VMs, etc. It is recommended to place the cluster servers in the same location and ensure high data transfer speed between them.

At the cluster level, the following parameters are set:

The cluster servers are called nodes. It is recommended that cluster nodes are homogeneous — have the same network settings, routing and software versions. For more information on node requirements, see the article Server requirements for the cluster.

VMmanager supports the use of overselling in the cluster. Overselling is the ability to place more VMs in a cluster than server resources allow. Overselling is available if the VMs in the cluster actually consume less resources than they were allocated for. Read more in Overselling.

The VMmanager Infrastructure version platform allows you to set up a high availability cluster. A high availability cluster is a group of servers that guarantees minimum downtime of virtual machines (VMs). If one of the cluster nodes loses connection with other nodes or the connected storage, VMmanager will start the recovery process - VM relocation: Read more in the section High availability clusters.

When you migrate a VM from VMmanager 5, a temporary cluster is created in the platform. A temporary cluster is a cluster with limited functionality to temporarily host VMs for the migration period. The temporary cluster includes VMmanager 5 cluster nodes. The restrictions are listed in the article Migration from VMmanager 5 to VMmanager 6.

Storages

Storage is the space where the files of the VM disks are located. Storage can be:

  • local — the files are located on the cluster node;
  • network — the files are located on an external server or a group of servers.

Several storages can be connected to the same cluster at the same time. The platform allows you to specify flexible settings for allocating VMs to storages.

For more details on supported storage types, see the article Storage types.

Platform

A platform server (server with VMmanager, master server) is a separate physical or virtual server on which the VMmanager software is installed. The platform server performs the functions of virtual and network resource management. To ensure stable operation, the server with the platform should not be used as a cluster node. Read more in Server requirements.