Virtualization

In accordance with Moore's Law, today's accelerated development of information technology and the penetration of virtualization technology makes it possible to break the traditional and typically inefficient "one-application-server-one" approach. Different applications have different kind of workloads imposed on the servers. While a typical file server has only a few percent of CPU load, in case of a hard-loaded database server up to 80% or more CPU load may occur. These workloads can be easily distributed and balanced in virtualized environment.

Using virtualization technologies make available the following advantages compared to the traditional approach:
Virtualizációs technológiák alkalmazásával az alábbi előnyök érhetők el szemben a tradícionális megközelítéssel:

• Optimizing the utilization of hardware resources
• Less hardware is required for these systems to serve
• Lower data center costs (electricity, air conditioning, etc.).
• Reduced space requirements in the data center
• Decreased the cost and time-frame of planned / unplanned downtime
• Increase availability
• Hardware independent
• Easier resource-management

Brief overview of the different aspects of virtualization:

Application-level virtualization

• The virtualiazation is realized not in OS-level
• Cygwin
  • Realizing Posix/GNU programming environment in Windows OS
  • Porting softwares developed in UNIX/Linux environment to Windows OS
• Wine
  • Realizing Windows APIs and some kernel functions in Linux and X11 environment

Operating system-level virtualization

• Realizing several program executing environment separated from each other, within one OS
• It complements the base OS to be able to create multiple VE* within itself
• Actually these VEs are the virtual copies of the same OS
• Unable to run a different OS
• Only 1-3% performance overhead
• Virtuozzo (Virtual Private Server)
• Jails (limited, secure access to the resources of the base OS)

* VE: Virtual Environment

Emulation

• Simulating a physical machine’s structure partly or wholly on another physical machine
• C64, Amiga, Super Nintendo, Playstation etc. emulators
• Real time transformation of the virtual environment instructions into the physical environment instructions by software
• No need for any modification on any OS
• Any hardware component can simulated by its use (even if it does not exist)
• Performance problems may occur

 
API Emulation

• It allows the host OS to run different OSs in the virtual system
• Host OS APIs (almost) one-to-one mapping of the guest OS with the appropriate library
• VMware
• MS VirtualPC and MS Virtual Server 2005

Paravirtualization

• Virtual machines can directly communicate with the hardware
• The host OS provides direct access to the hardware via API
• The guest OS must be prepared for this (porting)
• Low ~5% performance overhead
• User Mode Linux
  • Virtualizing Linux systems in Linux environment
  • Part of the Linux-kernel for today
• XEN
  • Virtualizing Linux, FreeBSD, Windows XP, Windows 2003 Server etc.