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Contents
• Virtualization - Definition, Types of Virtualization
• Server Virtualization - What ? How ? Why ?
• Server Virtualization - Limitations & Risks
• List of Sources
Virtualization : Definition• Virtualization, in computing, refers to the act of creating a
virtual (rather than actual) version of something, including but not limited to a virtual computer hardware platform, operating system (OS), storage device, or computer network resources.
• Virtualization began in 1960s mainframe computers as a method of logically dividing the system resources provided by mainframes between different applications. Since then, the meaning of the term has broadened
Virtualization : Types• Software
• OS Level Virtualization
• Application Virtualization
• Service Virtualization
• Memory
• Memory virtualization, aggregating random-access memory (RAM) resources from networked systems into a single memory pool
• Virtual memory, giving an application program the impression that it has contiguous working memory, isolating it from the underlying physical memory implementation
Virtualization : Types• Storage
• Storage virtualization, the process of completely abstracting logical storage from physical storage
• Distributed file system, any file system that allows access to files from multiple hosts sharing via a computer network
• Virtual file system, an abstraction layer on top of a more concrete file system, allowing client applications to access different types of concrete file systems in a uniform way
• Storage hypervisor, the software that manages storage virtualization and combines physical storage resources into one or more flexible pools of logical storage
• Virtual disk drive, a computer program that emulates a disk drive such as a hard disk drive or optical disk drive
Virtualization : Types• Data
• Data virtualization, the presentation of data as an abstract layer, independent of underlying database systems, structures and storage
• Database virtualization, the decoupling of the database layer, which lies between the storage and application layers within the application stack over all
• Network
• Network virtualization, creation of a virtualized network addressing space within or across network subnets
• Virtual private network (VPN), a network protocol that replaces the actual wire or other physical media in a network with an abstract layer, allowing a network to be created over the Internet
Server Virtualization : What ? & How ?
• Server virtualization can be defined as the conversion of one physical server into several individual & isolated virtual spaces that can be taken up by multiple users as per their respective requirements.
• There are three ways to create virtual servers:
1. Full virtualization
2. Para-virtualization
3. OS-level virtualization
• They all share a few common traits. The physical server is called the host. The virtual servers are called guests. The virtual servers behave like physical machines. Each system uses a different approach to allocate physical server resources to virtual server needs
Full Server Virtualization• Full virtualization uses a special
kind of software called a hypervisor. The hypervisor interacts directly with the physical server's CPU and disk space. It serves as a platform for the virtual servers' operating systems. The hypervisor keeps each virtual server completely independent and unaware of the other virtual servers running on the physical machine. Each guest server runs on its own OS -- you can even have one guest running on Linux and another on Windows.
Full Server Virtualization• The hypervisor monitors the
physical server's resources. As virtual servers run applications, the hypervisor relays resources from the physical machine to the appropriate virtual server. Hypervisors have their own processing needs, which means that the physical server must reserve some processing power and resources to run the hypervisor application. This can impact overall server performance and slow down applications
Para Server Virtualization• The para-virtualization approach
is a little different. Unlike the full virtualization technique, the guest servers in a para-virtualization system are aware of one another. A para-virtualization hypervisor doesn't need as much processing power to manage the guest operating systems, because each OS is already aware of the demands the other operating systems are placing on the physical server. The entire system works together as a cohesive unit.
OS-Level Virtualization• An OS-level virtualization approach
doesn't use a hypervisor at all. Instead, the virtualization capability is part of the host OS, which performs all the functions of a fully virtualized hypervisor. The biggest limitation of this approach is that all the guest servers must run the same OS. Each virtual server remains independent from all the others, but you can't mix and match operating systems among them. Because all the guest operating systems must be the same, this is called a homogeneous environment.
Server Virtualization : Why ?
• Server virtualization conserves space through consolidation. It's common practice to dedicate each server to a single application. If several applications only use a small amount of processing power, the network administrator can consolidate several machines into one server running multiple virtual environments. For companies that have hundreds or thousands of servers, the need for physical space can decrease significantly.
Server Virtualization : Why ?• Server virtualization provides a way for companies to
practice redundancy without purchasing additional hardware. Redundancy refers to running the same application on multiple servers. It's a safety measure -- if a server fails for any reason, another server running the same application can take its place. This minimizes any interruption in service. It wouldn't make sense to build two virtual servers performing the same application on the same physical server. If the physical server were to crash, both virtual servers would also fail. In most cases, network administrators will create redundant virtual servers on different physical machines.
Server Virtualization : Why ?
• Virtual servers offer programmers isolated, independent systems in which they can test new applications or operating systems. Rather than buying a dedicated physical machine, the network administrator can create a virtual server on an existing machine. Because each virtual server is independent in relation to all the other servers, programmers can run software without worrying about affecting other applications.
Server Virtualization : Why ?• Server hardware will eventually become obsolete, and
switching from one system to another can be difficult. In order to continue offering the services provided by these outdated systems (sometimes called legacy systems) a network administrator could create a virtual version of the hardware on modern servers. From an application perspective, nothing has changed. The programs perform as if they were still running on the old hardware. This can give the company time to transition to new processes without worrying about hardware failures, particularly if the company that produced the legacy hardware no longer exists and can't fix broken equipment.
Server Virtualization : Why ?• An emerging trend in server virtualization is called migration.
Migration refers to moving a server environment from one place to another. With the right hardware and software, it's possible to move a virtual server from one physical machine in a network to another. Originally, this was possible only if both physical machines ran on the same hardware, operating system and processor. It's possible now to migrate virtual servers from one physical machine to another even if both machines have different processors, but only if the processors come from the same manufacturer.
Server Virtualization : Limitations
• There's a limited amount of disk space and CPU Power available on physical servers. Too many virtual servers could impact the server's ability to store & process data.
• Another limitation is migration. Right now, it's only possible to migrate a virtual server from one physical machine to another if both physical machines use the same manufacturer's processor. If a network uses one server that runs on an Intel processor and another that uses an AMD processor, it's impossible to port a virtual server from one physical machine to the other.
Server Virtualization : Security Risks
• Blue Pill : This occurs when a virtual machine masquerades as a hypervisor by installing itself on a host machine. As a result, resource allocations and interactions between virtual OS instances are controlled by the virtual machine acting as an imposter.
• SubVirt : Is a VM rootkit that positions itself on the physical machine. It then monitors and records the activity of the VM. As a result, it disguises when the system is compromised and also may involve other threatening programs like spyware or keystroke loggers.
Server Virtualization : Security Risks
• Denial-of-Service : This is a virtual machine infrastructure attack that allows a single or multiple VMs to consume all of the resources that are contained within the host machine. Thus, these resources would not be available for other VMs.
• Trojan : In this case, a hacker compromises the virtual machine manager, which allows them to control the applications and operating systems that are found on the machines, which is generally not addressed by anti-virus software.
List of Sources• Botelho, Bridget. "AMD pushes VMware et al. to broaden live migration."
SearchServerVirtualization. Aug. 29, 2007. Retrieved on March 18, 2008. http://articles.techrepublic.com.com/5100-10879_11-6074941.html
• McAllister, Neil. "Server virtualization." InfoWorld. Feb. 12, 2007. Retrieved March 12, 2008. http://www.infoworld.com/article/07/02/12/07FEvirtualserv_1.html
• Ou, George. "Introduction to server virtualization." Tech Republic. May 22, 2006. Retrieved March 17, 2008. http://articles.techrepublic.com.com/5100-10879_11-6074941.html
• Perilli, Alessandro. "Step-by-step virtualization: Addressing all phases of adoption." SearchServerVirtualization. June 1, 2006. Retrieved March 18, 2008. http://searchservervirtualization.techtarget.com/tip/0,289483,sid94_ gci1191541,00.html
• Singh, Amit. "An Introduction to Virtualization." Kernelthread.com. Retrieved March 18, 2008. http://www.kernelthread.com/publications/virtualization/
List of Sources• Stansberry, Matt. "CIO primer: Virtualization basics."
SearchServerVirtualization. Jan. 4, 2006. Retrieved March 18, 2008.
• Margaret Rouse, WhatIs.com, http://searchservervirtualization.techtarget.com/definition/server-virtualization
• Roger Grimes, http://www.infoworld.com/article/2614369/security/the-5-cloud-risks-you-have-to-stop-ignoring.html
• cmeier and mnovellino, http://cybersecurity.mit.edu/2013/09/virtualization-awareness-and-security-threats/
