Virtualization Comparison

 

Three Types of Virtualization Technologies:
  • OS Virtualization (Containers)
    Virtualizes the operating system
  • Hardware Virtualization (Bare Metal)
    Virtualizes access to hardware
    resources
  • Application Virtualization (Cloud)
    Virtualizes individual applications across multiple hardware objects

Using the Right Virtualization Technology for the Job

As with any IT project, no single solution works for all situations. This is especially true in the case of virtualization, because technology professionals implement virtualization technologies for different reasons with different goals and in very different environments.

Choosing the correct approach largely depends on the task, goal, and environment. This document will focus on when to use OS virtualization (containers) and when to use hardware virtualization (hypervisor-based virtual machines).

Understanding OS Virtualization and Bare Metal (Hypervisor) Virtualization

Below is a side-by-side comparison of OS virtualization (left) and bare metal-based virtualization (right) architectures.

Figure 1: Virtualization Architectures
OS Virtualization
VE1 VE2 VE3

OS Virtualization Layer
Standard Host OS
Hardware
Bare Metal
VM1
OS VM2
OS VM3
OS

Virtual Hardware Virtual Hardware Virtual Hardware
Virtual Machine Monitor
Hypervisor OS
Hardware
Table 1: Technology Components
Component Description
Vitual Environment Homogenous OS with a defined set of resources
Vitualization Layer Emulates host OS
Standard Host OS Fully functional OS optimized for application performance
Component Description
Vitual Machine Generic computer with a
defined set of resources
Virtual Machine Monitor Emulates generic hardware
Hypervisor Fully functional OS optimized for hardware emulation

Important Considerations

The right technology for your situation depends on a range of factors, including your current environment, cost considerations, management goals, and performance requirements. The two tables below outline important considerations for each technology and highlight scenarios in which each technology is more suitable.

Figure 2: Important Considerations
  OS Virtualization Hypervisor Virtualization
Performance Native use of performance acceleration technologies and Operating Systems optimization algorithms, including file system and CPU caches, across virtual environments Optimized for performance of the virtual computer, but application performance is slower due to emulated device drivers and a lack of cross-OS coordination
Manageability Drastically reduces the number of OSes and related management costs Vast array of OSes you can choose to run. Management is done via usual methods of a regular dedicated server with similar OS.
OS Updates & Upgrades Single update or upgrade across all virtual environments Requires separate update or upgrade of each individual virtual machine
Consolidation Ratioy

(average) 20:1 consolidation ratio

VE contains only the subset of the OS needed for isolation and control, does not experience any performance overhead, and safely shares all common objects across all VEs

(average) 7:1 consolidation ratio

Each VM contains a full OS copy and experiences performance overhead
Single Point of Failure Standard Host OS or Hardware Node - Can effect all Virtual Environments on a Hardware Node due to OS or Hardware failure Hypervisor OS - Can only effect the individual Hypervisor Environment. Hardware failure would effect all Hypervisor Environments on node.

Comparing Virtualization Technologies & Products

Table 3: Best Scenario for Each Technology OS Containers
OS Containers Hypervisor Virtual Machines
Homogenous Consolidation
Better consolidation ratios with lower management and infrastructure cost 		Heterogeneous Consolidation
Mix multiple OSes on a server reducing hardware costs
Resource Intensive Workloads
Fully uses OS/application optimizations and preserves application performance 		Development Environment
Mix multiple OSes on a server
Software as a Service (SaaS)
Multiple instances of an application can be quickly deployed across isolated virtual environments and upgraded simultaneously 		Legacy OS Consolidation
Support for legacy OSes
Virtual Desktop Infrastructure
Substantially more clients per server and easier deployment of updates and upgrades. Lower licensing cost per VDI.		 Green Computing
Less hardware, resulting in less space, power, and people costs through higher consolidation ratios
Green Computing
Less hardware, resulting in less space, power, and people costs through higher consolidation ratios 		 

Comparing the Leading Virtualization Products

The previous sections only address the broad technologies without going into details of specific products. As with all technologies, the solution´s specific design and implementation make a significant difference on whether or not the technology works as promised. Therefore, it is important to compare the leading vendors representing each type of technology. Additionally, there are a number of features, such as backup and management, that must be taken into consideration when comparing specific products. Parallels Virtuozzo and Parallels Bare Metal Server are the leading OS Virtualization andHypervisor Virtualization solutions (respectively) on the market today. Below is a high level feature comparison.
Table 4: Feature Comparison - Parallels Virtuozzo vs.Parallels Bare Metal Server
    Virtuozzo Bare Metal
Scalability Consolidation Ratio 20:1 7:1
VM/Container Scalability Scales to full resources of server Scales to full resources of server
Performance Dynamic Resource Management Yes

Dynamic Allocation of CPU, Memory, & I/O 		Partial

Disk space and memory change requires reboot
CPU Architectures x86, x64, Itanium x86, x64
Performance Overhead 1-3% up to 50%1
Management Live Migration Yes2 Yes
Time Required to Provision One Virtual Server 30 sec-1 minute 5-10 minutes
Global Patching of VEs or VMs Yes No
Support for SAN, iSCSI, etc. Yes Yes
Physical to Virtual (P2V) Yes Yes
Shared Storage Required for Live Migration No Yes
High Availability Cluster Support Yes3 Yes
Virtual Server Backup Yes Yes
Price Per Container Starts @ $9.95/mo Starts @ $69.95/mo

  • 1Customers report up to 50% overhead depending on the number and types of applications running inside the virtual machine and the total number of virtual machines. Each additional virtual machine's OS and application(s) have a cumulative effect on the total overhead and resulting server performance.
  • 2Only available on Linux. Windows Live Migration will be available in a future release.
  • 3Virtuozzo requires Microsoft Clustering Services or Red Hat Cluster Service.