A VM (virtual machine) server refers to a physical server that is partitioned to create and run multiple virtual machine instances. The full form of VM in the context of servers stands for Virtual Machine.A virtual machine (VM) is an emulation of a computer system that runs its own operating system (OS) and applications like a real computer. A VM allows multiple OS environments to co-exist on the same computer, in strong isolation from each other.
Benefits of Using VM Servers
Using VM servers provides several key benefits:
- Increased Efficiency – Multiple VMs can operate independently on the same physical server, increasing utilization.
- Isolation – VMs are isolated from each other and the underlying host for increased security.
- Portability – VMs can be easily migrated between host servers.
- Scalability – It is easy to provision new VMs as computing resource needs change.
- Backups and Recovery – VMs can be backed up or cloned as needed for backup/restore purposes.
How VM Servers Work
VM servers use a bare-metal (native) hypervisor to create independent guest VMs sharing hardware:
- The hypervisor creates and runs the virtual machines – it allocates resources dynamically and isolates VMs.
- The guest operating system runs inside each VM container – like Linux, Windows, etc.
- Virtual hardware/devices like vCPU, vRAM, Storage, etc emulate real hardware for VMs.
Popular hypervisors used include VMware ESXi, Microsoft Hyper-V, Citrix XenServer etc. Multiple VMs running different workloads can operate together on the same host, sharing the physical resources between them via the hypervisor.
Components of a VM Server
The key components that make up a VM server setup are:
- Host Server Hardware – The underlying physical server provides the compute power – CPU, memory, storage and network resources for running the VMs.
- Hypervisor Software – The hypervisor software creates the virtualization layer to manage and isolate VMs.
- Guest Operating Systems – Different guest OS like Windows, Linux run application workloads inside each VM.
- Virtual Hardware – Virtual components like vCPU, vRAM, vNIC, virtual disks emulate the physical hardware.
Types of VM Servers
There are two main types of VM Servers:
Bare-Metal (Native) Hypervisors
These hypervisors run directly on the host server hardware with no base operating system – Type 1 Hypervisors. Examples include:
- VMware ESXi
- Citrix XenServer
- Microsoft Hyper-V
They provide higher performance by accessing the hardware directly, but have limited management OS capabilities.
These hypervisors run as an application on top of the host OS, with the VMs as a process – Type 2 Hypervisors. Examples include:
- VMware Workstation
- Oracle VirtualBox
- Parallels Desktop
They are easier to install, but provide less isolation and lower performance than bare-metal hypervisors.
Virtual Machine Provisioning
There are two approaches to provisioning VMs on a server:
- Resources like CPU, RAM, Storage are allocated to a VM at creation time
- The VM has guaranteed resource availability
- However, the resources may sit idle if the VM is powered off
- Actual resource allocation happens on-demand when VM requires them
- Allows for VM overcommit to improve hardware utilization
- However, resource contention can happen when multiple VMs compete for resources
A balance of both approaches is ideal for most uses. Resources like vCPU and vRAM are generally allocated pre-defined, while storage can be thin-provisioned to save space.
- VM servers allow multiple virtual machine instances to efficiently utilize the same physical server hardware.
- This is achieved through a hypervisor that creates independent VMs that are isolated from each other.
- VMs can run different guest operating systems and workloads in strong isolation.
- VM server virtualization provides portability, scalability, and reliability benefits at data centers.
The full form of VM in the context of servers is Virtual Machine. VM servers run hypervisor software on the physical hardware that allows multiple guest virtual machine environments to share resources and co-exist isolated from each other.
This virtualization approach provides better hardware utilization and is easier to manage at scale than separate physical servers. Leading hypervisors like VMware ESXi allow running mixed operating system and application workloads efficiently on the same infrastructure. With capabilities like live migration, replication and high availability, VM servers enable consolidating compute resources at data centers for better operational efficiency.
Frequently Asked Questions
- What is a VM server used for?
A VM server allows data centers to consolidate multiple application workloads on shared infrastructure for better utilization. It reduces hardware costs and is easier to manage.
- What are the benefits of a VM server?
Benefits include improved efficiency, isolation, portability, scalability and easier backup & recovery of virtual machines.
- What hardware is required for a VM server?
A VM server requires powerful multi-core CPUs, plenty of RAM, network connectivity and shared storage like SAN or NAS to host the multiple virtual machines.
- What software runs on a VM server?
The VM server hardware runs a hypervisor like ESXi to create, run and manage the virtual machines which in turn run guest operating systems & applications.
- What are examples of popular VM server hypervisors?
VMware ESXi, Microsoft Hyper-V and Citrix XenServer are popular bare-metal hypervisors while VMware Workstation and Oracle VM VirtualBox are popular hosted hypervisor options.
- How does VM server virtualization work?
The hypervisor software partitions physical resources to create isolated guest VM environments sharing the same host hardware, providing features like live migration and resource allocation.
- How is a VM server different from a regular server?
A regular physical server runs a single OS directly on the hardware. A VM server runs a hypervisor to allow that same server hardware to run multiple virtual machine OS instances in isolation.
- Can you run VMs locally without a server?
Yes, hypervisors like VirtualBox can run VMs locally on desktops & laptops. But VM servers allow centralized management at scale, high availability, automated provisioning and load balancing of VMs.
- What are the different types of VM servers?
The types are – bare-metal (Type 1) hypervisors that run directly on server hardware, and hosted (Type 2) hypervisors that run as an application within the host OS environment.
- How is VM hardware different from physical hardware?
The VM hardware components like vCPU, vRAM, vNIC and virtual disks are emulated in software. This virtual hardware allows VMs to function like real machines but the actual resources come from the underlying physical server hardware.
- Is VM server virtualization better than containers?
Both approaches have trade-offs – VMs provide stronger isolation but consume more resources. Containers are lightweight and share the host OS kernel but pose security risks. Many environments use a mix of VMs and containers.
- What are para-virtualized devices in VM servers?
Para-virtualization improves virtual device performance by replacing emulated devices with smarter hypervisor-aware virtual drivers that can optimally access physical hardware resources.
- How are resources allocated to VMs on a server?
IT administrators can choose to pre-allocate vCPU & vRAM capacity to VMs or dynamically allocate resources only when needed depending on the application profiles. Disk storage is generally thin provisioned.
- What is VM overcommit and what are its risks?
Overcommit refers to assigning more cumulative VM hardware capacity than physically available on the server. It improves utilization but can lead to contention & performance issues when VMs spike.
- What hardware considerations are important for a VM server?
For best performance, choose servers with multi-core CPUs, high RAM and cache capacity, fast internal storage, 10Gbps+ network adapters and enterprise-grade hardware components.
- How is vSphere different from a VM server?
The VMware vSphere product suite includes the ESXi hypervisor to create VMs but also adds management capabilities on top with components like vCenter Server and vSphere Client.
- Is it better to run one VM per host or multiple?
In most cases running multiple properly sized VMs per host allows maximizing hardware utilization. One VM per host is only common for purposes like security, compliance or performance testing.
- How are VM licenses calculated?
Public cloud platform VMs are billed based on hourly metering of capacity used. For on-prem VM servers, hypervisor hosts and OS/app licenses are based on metrics like per socket, core or VM counts or raw capacity.
- What are the disaster recovery options for VM servers?
VM replication, backup & restore capabilities allow recovering VM workloads to standby hosts. Site recovery to secondary facilities and integration with cloud DR are also commonly employed.