What is a virtual machine?

What it means

To the software inside, a VM looks like an ordinary server. You install Windows or Linux on it, add your applications and sign in as usual. Underneath, the hypervisor, the core of virtualization, presents slices of real hardware as a virtual disk, memory and network connection.

Because the whole machine is stored as files, it can be handled in ways a physical server cannot:

• Snapshots: a saved point in time that you can return to, handy before an update.
• Whole-machine backups: the entire server is copied, so it can be restored in one piece.
• Live migration: a running VM moves from one physical server to another without being shut down.

A container shares the host's operating system kernel and packages only an application and what it needs, so it is smaller and starts faster. A VM carries a full system of its own and is more strongly isolated.

Why it matters to a business

• Hardware independence: a VM can move to new hardware without rebuilding the server.
• Fast recovery: a restored VM brings back the system, settings and data together.
• Maintenance without downtime: with shared or replicated storage, live migration lets a host be patched or repaired while its machines keep running elsewhere.
• Snapshots are not backups: a snapshot sits on the same storage as the VM, so it will not help if that storage fails.

How this shows up in our work

On Proxmox VE we run virtual machines and LXC containers side by side. We back VMs up with Proxmox Backup Server and test the restores. Several hosts joined in a cluster make live migration possible.

Learn more

• Virtual machine on WikipediaA neutral explanation of what a VM is and the main kinds, useful for readers new to the idea.
• Hypervisor on WikipediaDescribes the software that creates and runs VMs, for readers who want to see how it works.
• Proxmox VE documentationThe official guide to creating, backing up and migrating VMs, aimed at administrators.