Computer Science
Hypervisors
Hypervisors are software or firmware that create and run virtual machines (VMs) by separating the physical hardware from the operating system. They enable multiple operating systems to run on a single physical machine, allowing for efficient use of resources and improved flexibility in managing and deploying computing environments. Hypervisors are commonly used in server virtualization and cloud computing.
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11 Key excerpts on "Hypervisors"
eBook - PDF- K. Chandrasekaran(Author)
- 2014(Publication Date)
- Chapman and Hall/CRC(Publisher)
175 Virtualization the technology that enables the virtual environment also gets attention in industries and academia. The virtual environment can be created with the help of a software tool called Hypervisors . Hypervisors are the software tool that sits in between VMs and physical infrastructure and provides the required virtual infrastructure for VMs. Generally, the virtual infrastruc-ture means virtual CPUs (vCPUs), virtual memory, virtual NICs (vNICs), virtual storage, and virtual I/O devices. The Hypervisors are also called VMM. They are the key drivers in enabling virtualization in cloud data cen-ters. There are different Hypervisors that are being used in the IT industry. Some of the examples are VMware, Xen, Hyper-V, KVM, and OpenVZ. The different types of Hypervisors, some popular Hypervisors in the market, and security issues with recommendations are discussed in this section. 7.4.1 Types of Hypervisors Before Hypervisors are introduced, there was a one-to-one relationship between hardware and OSs. This type of computing results in underutilized resources. After the Hypervisors are introduced, it became a one-to-many relationship. With the help of Hypervisors, many OSs can run and share a single hardware. Hypervisors are generally classified into two categories: 1. Type 1 or bare metal Hypervisors 2. Type 2 or hosted Hypervisors The major difference between these two types of Hypervisors is that type 1 runs directly on the hardware and type 2 on host OS. Figures 7.13 and 7.14 illustrate the working of type 1 and type 2 Hypervisors, respectively. Type 1 hypervisor is also known as bare metal or native hypervisor. It can run and access physical resources directly without the help of any host OS. Here, the additional overhead of communicating with the host OS is reduced and offers better efficiency when compared to type 2 Hypervisors. This type of Hypervisors is used for servers that handle heavy load and require more security.
eBook - PDF- Greg Tomsho(Author)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
• The hypervisor is the part of virtualization software that creates and monitors the virtual hardware environment that allows multiple VMs to share physical hardware resources. On a host computer, the hypervisor acts somewhat like an OS kernel, but instead of scheduling processes for access to the CPU and other devices, it schedules VMs. It’s sometimes called the virtual machine monitor (VMM). There are two types of Hypervisors: ❍ ❍ A type 1 hypervisor implements OS virtualization by running directly on the host computer’s hardware and controls and monitors guest OSs. It also controls access to the host’s hardware and provides device drivers for guest OSs. Also called bare-metal virtualization, it’s used mainly for server virtualization and virtual desktop infrastructures in datacenters. Examples include VMware vSphere, Citrix Hypervisor, and Microsoft Hyper-V Server. ❍ ❍ A type 2 hypervisor implements OS virtualization by being installed in a general-purpose host OS, such as Windows 10 or Linux, and the host OS accesses host hardware on behalf of the guest OS. Also called hosted virtualization, it’s used mostly for desktop virtualization solutions. Examples include VMware Player and Workstation, Oracle VirtualBox, and OpenVZ for Linux. • A virtual disk consists of files on the host computer that represent a virtual machine’s hard drive. Figure 8-1 A Windows 10 host with Linux and macOS virtual machines MODULE 8 Virtualization and Cloud Computing Fundamentals 317 Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
- Sara Perrott(Author)
- 2022(Publication Date)
- For Dummies(Publisher)
It also simplified recovery efforts when configured properly because VMs on a failed host could be transferred to another host. You sometimes hear Hypervisors referred to as hosts and virtual machines referred to as guests. If you run into this terminology, don’t let it confuse you. These terms are used across all types of virtualization technologies. Type 1 and Type 2 Hypervisors Before I dive into the difference between Type 1 and Type 2 Hypervisors, I want to make sure that you understand what a hypervisor is. The hypervisor is essentially a process that allows you to create, run, and manage VMs. The hypervisor is ultimately responsible for presenting resources to the VMs that are running on it, including CPU, RAM, networking, and storage. Most of the Hypervisors let you overprovision VMs, meaning that you can assign resources that are not necessarily available. This may work for you if your work-loads are very small, but if there are spikes in the workloads, or if VMs take too many resources, then the hypervisor could become starved for resources, which could impact all your VMs that are running on that hypervisor. For this reason, I recommend not over-provisioning your VMs. What Is Hyper-V? CHAPTER 1 What Is Hyper-V? 597 Type 1 Hypervisors Type 1 Hypervisors are also referred to as bare-metal Hypervisors. This is because the software for the hypervisor can run directly on the host system’s hardware. Type 1 Hypervisors provide the best performance and security of the Hypervisors, but some of them are more complex that others to set up. Here are some examples of the more common Type 1 Hypervisors: » Microsoft Hyper-V » VMware ESXi » Oracle VM Server » KVM » Citrix XenServer Type 2 Hypervisors Type 2 Hypervisors are referred to as hosted Hypervisors. They require an operating system to be able to install and run.
eBook - PDF- Jill West(Author)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
These Hypervisors function as shown earlier in Figure 2-2, where the hypervisor is installed over an existing OS as an application, and then guest OSs are installed inside the hypervisor. This is called a type 2 hypervisor. Module 2 Virtual Hardware 37 Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. By contrast, a type 1 hypervisor is installed directly on the firmware of the physical machine and is sometimes erroneously referred to as a “bare-metal” hypervisor. In reality, a type 1 hypervisor is itself a minimal operating system, many of which are built on a Linux kernel. Like any OS, the hypervisor relies on firmware to enable communication with the underlying hardware. See Figure 2-3. Examples of a type 1 hypervisor include ESXi by VMware (vmware.com), Hyper-V by Microsoft (microsoft.com), and Citrix XenServer (xenserver.org) powered by the open-source Xen Project hypervisor (xenproject.org).
eBook - ePubCloud Computing Simplified
Explore Application of Cloud, Cloud Deployment Models, Service Models and Mobile Cloud Computing (English Edition)
- Surbhi Rastogi(Author)
- 2021(Publication Date)
- BPB Publications(Publisher)
In server virtualization, the physical server is divided into multiple virtual servers. All these servers are different and work like unique devices. They seem to be real physical devices to the users. These servers possess a sufficient amount of computing power to perform their tasks effectively. The central server administrator uses a software to divide the physical server into more than one virtual environments. Each virtual environment runs its own operating system independently. All the physical resources of the central server are also shared among the virtual servers. The physical server is known as the host and the virtual servers are termed as the guests. The following figure depicts server virtualization:Figure 6.5: Server virtualizationServer virtualization performs its task by partitioning software from hardware using hypervisor. As we previously discussed, hypervisor is a layer between the hardware and the operating system. Hypervisors are of different types and serve different purposes. We mostly use two types of Hypervisors, namely Type 1 and Type 2. With Type 1, users can directly work on the server. It is also known as bare-metal hypervisor. The Type 1 hypervisor enables us to virtualize the hardware platform which can be further used by the virtual machine. Type 2 hypervisor runs as a software layer on the top of the host operating system. It is used for testing purposes.After the server is virtualized, the organization can use the resources of the server for other tasks. All virtual servers can utilize the resources of the server. Organizations should determine the resources and the quantity that can be allocated to each virtual machine. They should monitor the system to track the performance of the resources such as the memory, disk usage, and processor overload. Each virtual server can be dedicated to perform a specific task instead of buying a physical server for each task. This increases the efficiency of the organization.Virtualization software is used to create virtual servers. Organization can deploy Hypervisors like Microsoft Hyper-V and VMware vSphere or virtualization tools for this. Central server is virtualized and its resources are utilized by organization to increase the efficiency of the system.
eBook - PDF- Palmer, Greg Tomsho(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
On a host computer, the hypervisor acts somewhat like an OS kernel, but instead of sched-uling processes for access to the CPU and other devices, it schedules VMs. It ’ s sometimes called the virtual machine monitor (VMM) . There are two types of Hypervisors: A type 1 hypervisor implements OS virtualization by running directly on the host computer ’ s hardware and controls and monitors guest OSs. It also controls 8 Virtualization Fundamentals 359 Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 access to the host ’ s hardware and provides device drivers for guest OSs. Also called bare-metal virtualization , it ’ s used mainly for server virtualization in data centers. Examples include VMware ESX Server, Citrix XenServer, and Microsoft Hyper-V Server. A type 2 hypervisor implements OS virtualization by being installed in a general-purpose host OS, such as Windows 10 or Linux, and the host OS accesses host hardware on behalf of the guest OS. Also called hosted virtualization , it ’ s used mostly for desktop virtualization solutions. Examples include VMware Player and Workstation, Oracle VirtualBox, and OpenVZ for Linux. • A virtual disk consists of files on the host computer that represent a virtual machine ’ s hard drive. • A virtual network is a network configuration created by virtualization software and used by virtual machines for network communication. • A snapshot is a partial copy of a VM made at a particular moment; it contains changes made since the VM was created or since the last snapshot was made. It is used to restore the VM to its state when the snapshot was taken. Figure 8-2 illustrates the virtualization process. The hypervisor on the host is running two VMs connected to a virtual network, which in turn has a connection to the physical network so that the VMs can communicate on it.
eBook - ePubMobile Cloud Computing
Foundations and Service Models
- Dijiang Huang, Huijun Wu(Authors)
- 2017(Publication Date)
- Morgan Kaufmann(Publisher)
Fig. 2.7 B, a system VM provides a complete system environment that can support a “guest OS” with (probably) many user processes. It is placed between underlying hardware and conventional software, and it also provides ISA translation. Another alternate approach is using hosted VM, where virtualizing software is built on top of an OS.Figure 2.7 (A) Process Virtual Machine and (B) System Virtual Machine.A hypervisor (or VMM – Virtual Machine Monitor) is a software layer that allows several VMs to run on a physical machine. A “hypervisor” is the essence of the cloud technology that we all enjoy today. Nowadays, there exist many stable and feature-rich Hypervisors: RetHat KVM, VMware, Microsoft Hyper-V, Oracle VirtualBox, and Xen, to name several popular ones. One of the main differences between hypervisor platforms is their classification as “Type 1” or “Type 2” hypervisor, which are presented in Fig. 2.8 .Figure 2.8 The third virtualization classification.Type 1 Hypervisors directly run on the physical hardware. They control the hardware as well as manage the VMs. Type 1 Hypervisors are also termed bare metal Hypervisors. Type 2 Hypervisors run as an application on an existing OS (a.k.a., host OS), which is installed on the bare metal. Here, there is an added complexity of the guest OS calls needing to traverse via the host OS stack before they reach the hardware.Type 1 Hypervisor
Linux KVM [1] . A KVM (kernel-based VM) is a GNU/Linux based project developed for x86 machines. It operates with a loadable kernel module named kvm.ko, which turns the Linux kernel itself into a hypervisor and thus VMs have direct access to the hardware. KVM also contains processor-specific kernel modules such as kvm-intel.ko and kvm-amd.ko. Virt-manager and virsh applications are generally used to manage the VMs created using KVM. Virt-manager provides a GUI, whereas virsh is a command line utility.A commonly accepted misconception is that KVM is a Type 2 hypervisor that is hosted by the OS, and not a bare metal hypervisor. This is a persistent myth, but the truth is that KVM actually does run directly on x86 hardware. The interface makes it look like KVM is a hosted hypervisor running on the OS, but the VM is running on the bare metal – the host OS provides a launch mechanism for the hypervisor and then engages in a coprocessing relationship with the hypervisor. In a sense, it is taking over part of the machine and sharing it with the Linux kernel.
- Edouard Bugnion, Jason Nieh, Dan Tsafrir(Authors)
- 2022(Publication Date)
- Springer(Publisher)
In direct execution, the hypervisor sets up the hardware environment, but then lets the virtual machine instructions execute directly on the processor. As these instruction sequences must operate within the abstraction of the virtual machine, their execution causes traps, which must be emulated by the hypervisor. is trap-and-emulate paradigm is central to the design of Hypervisors; and • a machine simulator is typically implemented as a normal user-level application, with the goal of providing an accurate simulation of the virtualized architecture, and often runs at a small fraction of the native speed, ranging from a 5 slowdown to a 1000 slowdown, depending on the level of simulation detail. Machine simulators play a fundamental role in computer architecture by allowing the detailed architectural study of complex work- loads [36, 124, 153, 181]. 6 1. DEFINITIONS 1.3 Hypervisors A hypervisor is a special form of system software that runs virtual machines with the goal of minimizing execution overheads. When multiple virtual machines co-exist simultaneously on the same computer system, the hypervisor multiplexes (i.e., allocates and schedules) the physical resources appropriately among the virtual machines. Popek and Goldberg formalized the relationship between a virtual machine and hypervisor (which they call VMM) in 1974 as follows [143]. . . A virtual machine is taken to be an efficient, isolated duplicate of the real ma- chine. We explain these notions through the idea of a virtual machine monitor (VMM). As a piece of software, a VMM has three essential characteristics. First, the VMM provides an environment for programs which is essentially identical with the original machine; second, programs running in this envi- ronment show at worst only minor decreases in speed; and last, the VMM is in complete control of system resources.
eBook - PDF- Abraham Silberschatz, Peter B. Galvin, Greg Gagne(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
18.5 Types of VMs and Their Implementations 767 system calls and other interfaces for running programs, they create, run, and manage guest operating systems. In addition to running on standard hard- ware, they can run on type 0 Hypervisors, but not on other type 1 Hypervisors. Whatever the platform, guests generally do not know they are running on anything but the native hardware. Type 1 Hypervisors run in kernel mode, taking advantage of hardware pro- tection. Where the host CPU allows, they use multiple modes to give guest oper- ating systems their own control and improved performance. They implement device drivers for the hardware they run on, since no other component could do so. Because they are operating systems, they must also provide CPU schedul- ing, memory management, I/O management, protection, and even security. Frequently, they provide APIs, but those APIs support applications in guests or external applications that supply features like backups, monitoring, and secu- rity. Many type 1 Hypervisors are closed-source commercial offerings, such as VMware ESX, while some are open source or hybrids of open and closed source, such as Citrix XenServer and its open Xen counterpart. By using type 1 Hypervisors, data-center managers can control and man- age the operating systems and applications in new and sophisticated ways. An important benefit is the ability to consolidate more operating systems and applications onto fewer systems. For example, rather than having ten systems running at 10 percent utilization each, a data center might have one server man- age the entire load. If utilization increases, guests and their applications can be moved to less-loaded systems live, without interruption of service. Using snap- shots and cloning, the system can save the states of guests and duplicate those states—a much easier task than restoring from backups or installing manually or via scripts and tools.
eBook - PDFLarge Scale and Big Data
Processing and Management
- Sherif Sakr, Mohamed Gaber, Sherif Sakr, Mohamed Gaber(Authors)
- 2014(Publication Date)
- Auerbach Publications(Publisher)
As discussed throughout this chapter, a hypervisor is mainly responsible for running multiple virtual machines (VMs) on a single physical host. On the other hand, a virtualization suite comprises of various software compo-nents and individual Hypervisors that enable the management of many physical hosts and VMs. A management component typically issues commands to the hypervisor to create, destroy, manage, and migrate VMs across multiple physical hosts. Table 16.2 shows our taxonomy of four virtualization suites, vSphere 5.1 [59], Hyper-V [43], XenServer 6 [17], and RHEV 3 [50]. We compare the suites in terms of multiple features including the involved hypervisor, the virtualization type, the allowable maximum number of vCPUs per a VM, the allowable maximum memory size per a VM, and whether memory over-commitment, page sharing, and live migration are supported. In addition, we indicate whether the involved Hypervisors contain device drivers, and list some of the popular cloud vendors that utilize such Hypervisors. To elaborate on some of the features, live migration allows VMs to be seamlessly shifted from one VM to another. It enables many management features like maintenance, power-efficient dynamic server consolidation, and workload balancing, among others. Page Sharing refers to sharing identical memory pages across VMs. This renders effective when VMs use similar OS instances. Lastly, some Hypervisors eliminate entirely device drivers at guest OSs and provide direct com-munications between guest OSs and host OSs co-located with Hypervisors (similar to what we discussed in Section 16.8.3 about the Xen hypervisor). 525 Virtualizing Resources for the Cloud 16.9 CASE STUDY: AMAZON ELASTIC COMPUTE CLOUD Amazon Elastic Compute Cloud (Amazon EC2) is a vital part of Amazon’s cloud computing platform, Amazon Web Services (AWS). On August 25, 2006 Amazon launched EC2, which together with Amazon Simple Storage Service (Amazon S3), marked the change in the way IT was done.
eBook - PDF- April J. Wells(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
169 Chapter 8 Virtualization Computer Science is no more about computers than astronomy is about telescopes. —Edsger W. Dijkstra Virtualization, loosely translated, means an abstraction of computer resources. It is a technique used for hiding the physical characteristics of computing resources or a way of making multiple physical resources (storage devices or servers) appear as a single logical resource. Virtualization, however, is not necessarily a Grid-related concept. Far from it, in fact. Virtualization has been used extensively since at least the early 1960s and has been applied to many different aspects of computing. It has been used in entire computer systems component and components. Virtualization technologies are usually employed through the hiding of tech-nical details of the underlying components through encapsulation that creates an external interface to the underlying implementation. Recent developments in Grid technologies have renewed development in these technologies and refocused atten-tion on the concept. Platform virtualization is used to simulate virtual machines. Resource virtual-ization is used to simulate combined, fragmented, and simplified resources. In Grid-related information technology, virtualization can take on several meanings, depending on what is being virtualized. If computer hardware is what we are visualizing, then virtualization implies that we will use software to emulate either the hardware or an entire computer system environment other than the one on which the software is actually running. This virtualization of hardware is often referred to as a virtual machine . The term “virtual 170 n Grid Applications Systems Design machine” has been connected directly with Sun Microsystems’ Java programming language. That context defines an abstracted or conceptual machine rather than a real machine.
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