Terms Virtual Machines Fact Sheet T1: Host The underlying hardware systems that runs a virtual machine. T2: Virtual Machine Manager (VMM) Also known as a hypervisor, the VMM provides an interface that is identical to the host for guest utilization. T3: Hypervisors T3.1: Type 0 hypervisor Hardware based support for virtual machine creation and management via firmware. T3.2: Type 1 hypervisor Operating system like software designed to provide virtualization (eg VM Ware) T3.3: Type 2 hypervisor Applications that run on standard operating systems, but offer VMM features from guest operating systems. T4: Guest A process which uses a virtual copy of the host to run. Often this process is an operating system. T5: Paravirtualization An environment in which the guest operating system is modified to work with the VMM to optimize performance. T6: Minidisks Virtual disks that are allocated within a system s hard disk to host a virtual machine. T7: Garbage collection The practice of reclaiming memory from objects no longer in use and returning it to the system T8: Nested Page Tables (NPT): Each guest maintains page tables to translate virtual to physical addresses. The virtual machine manager maintains a NPT to represent guest s page table state. When a guest is on the CPU, the VMM makes the guest s NFT the active system page table. T9: Templating: one standard virtual machine image, including an installed and configured guest operating system and applications, is saved and used as a source for multiple running VMs. Other features include managing the patching of all guests, backing up and restoring the guests, and monitoring their resource use. T10: Live Migration: a feature provided by the VMM which moves a running guest from one physical server to another without interrupting its operation or active network connections. If a server is overloaded, live migration can thus free resources on the source host while not disrupting the guest.
Questions Q1: Who was the first to introduce virtual machines commercially and in what year did they do so? A1: IBM first introduced virtual machines commercially on their mainframes in 1972. Q2: What are IBM s three virtualization requirements? A2: A VMM must provide an environment that is easily identical to the original machine, programs running must show only minor performance defects, and the VMM must be in complete control of system resources. Q3: What is redundancy in relation to server virtualization used in a business environment. A3: The same application can be run on two or more servers in order to decrease the chance of a service interrupt if there is a problem with a server. Q4: What is the role of a hypervisor? A4: The hypervisor acts as a platform for a virtual server s operating system(s). It interacts with the physical CPU and disk space and keeps each virtual server independent. Q5: What is an emulator? A5: An emulator is software that allows applications written for one type of hardware run on a different type of hardware. An example of this would be an application that acts like an ipad that will run apps on a desktop/ Q6: What are the advantages of Virtual Machines (VM)? A6: The Host system is protected from Virtual Systems and Virtual Systems are protected from each other. VMs can also share the same hardware yet run different execution environments. The virtual machine can also be cloned, snapshotted, suspended, or resumed. Q7: Define System Development time and how Virtual Machines are involved. A7: System Development is when changes are made to the O/S thus preventing users from using the machine. This usually occurs at night or on late weekends. This problem can be cut down with Virtual Machines because multiple Operating Systems can run concurrently on a workstation. Consolidation can also occur, where two or more separate systems run under one system. This results in resource optimization and combined can create a more heavily used system.
Q8: Describe Trap to Emulate as used in Virtual Machines. A8: Trap to Emulate: Privileged instructions cannot be performed under guest mode so the Virtual Machine Manager takes control and emulates the action that was attempted by the guest kernel on the part of the guest. The control is then returned to the guest in user mode. Q9: Describe Binary Translation as it relates to Virtual Machines. A9: Binary Translation: If VCPU is in user mode, guest can run code natively. If guest VCPU is in kernel mode, VMM examines every instruction guest is about to execute. Special instructions are translated into a new set of instructions that then perform the equivalent task. Products like VMware use caching so if the same instruction is called upon twice, cached translation is used instead of the code being translated again. Q10: Explain how hardware assistance can increase a Virtual Machine's potential. A10: AMD V and Intel VT X both provide Virtual Machines with added modes which make the CPU multimode. New modes include guest and host or root and non root. Virtual Machine Manager enables host mode and defines characteristics for each guest Virtual Machine and then switches the system to guest mode, passing control of the system to a guest O/S that is running in the VM. In guest mode the virtualized O/S thinks it s running on native hardware and sees whatever devices are included in the host s definition of the guest. Q11: How are Type 0 Hypervisors different from Type 1 and Type 2 in terms of hardware? A11: Guests on type 0 hypervisors run on partitions of raw hardware, and can each be turned into a separate VMM with their own guest operating systems. Q12: What is the goal of Memory Management in virtualized environments? A12: Enable guests to behave and perform as if they had the full amount of memory requested even though they actually have less. Q13: For type 1 and type 2 hypervisors, how are guest root disks stored? What is the benefit of doing this? A13: The contents of the root disks are stored in one file that is essentially a disk image of the guest OS. It simplifies copying and moving guests by allowing the moving or copying of a single file. Q14: What does a network infrastructure need to understand about MAC Addresses for Live Migration to work?
A14: Unlike the MAC Addresses of a physical system, which are tied to physical hardware, the MAC addresses of virtualized systems need to be moveable for existing network connections to continue without resetting. Q15: How does a VMM migrate a guest? A15: The source VMM establishes a connection with the target VMM, and the target creates a new guest. The source then sends all read only memory pages to target followed by all read write pages to the target, marking them as clean. The source repeats sending read write pages to the target since some pages were more than likely modified by the guest and are now dirty. When the cycling of resending modified pages between source and target becomes very short, the source VMM freezes the guest, sends the VCPU's final state, sends other state details, sends the final dirty pages, and tells the target to start running the guest. Once the target acknowledges, the source terminates. Q16: What popular commercial application abstracts Intel X86? And what type of hypervisor does it use? A16: VMware Workstation, it uses Type 2 hypervisor. Q17: What type of file is created for each Java class when the compiler is ran? Will it run on any implementation of the Java Virtual Machine. A17: Bytecode output file, or the.class file, and it will run on any implementation of the JVM. Q18: How does the Java Virtual Machine automatically manage memory? A18: Garbage collection, it will reclaim memory from objects no longer in use. Q19: What type of hypervisor are applications that do not use hardware or host support? Do they know that virtualization is taking place? A19: Type 2 hypervisors, they do not know that virtualization is taking place. Q20: What is virtualization? A20: The method of providing a guest with a duplicate of a system's hardware.
Sources Cited Ahmad, Raja Wasim, Abdullah Gani, Siti Hafizah Ab. Hamid, Muhammad Shiraz, Feng Xia, and Sajjad A. Madani. Virtual machine migration in cloud data centers: a review, taxonomy, and open research issues. Journal of Supercomputing 71.7 (2015): 2473 2515. Print. Hoffman, Chris. "What Is a Virtual Machine?" MakeUseOf. Web Culture, 18 July 2012. Web. 01 Apr. 2016. "How Server Virtualization Works." HowStuffWorks. N.p., 02 June 2008. Web. 02 Apr. 2016. Silberschatz, Abraham, Peter B. Galvin, and Greg Gagne. "Virtual Machines." Operating System Concepts. N.p.: n.p., n.d. 711 40. Print. Slangen, Simon. "What Is The Java Virtual Machine & How Does It Work? [MakeUseOf Explains]." MakeUseOf. N.p., 2 Apr. 2012. Web. 03 Apr. 2016. <http://www.makeuseof.com/tag/java virtual machine work makeuseof explains/>. Enrique Paredes Morris Ballenger Kevin Goodenough Michael Anderson CS 308 Spring 2016