Nally we discuss two different classes of vm tech

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nally, we discuss two different classes of VM tech- nology from the standpoint of meeting the require- ments of the usage scenarios demanding good per- formance, high scalability, and strong isolation. 2.1 Usage Scenarios Virtual machine technologies are poised to be present throughout most computer systems. There are a number of exciting ideas to use VMs to secure work environments on laptops [18], ease manage- ment and improve utilization of large compute clus- ters, analyze unknown virus/work attacks in real- time [17], and debug difficult to track down sys- tem failures using time-travel [19]. However, to- day VM technology is predominantely used by: (1) programmers on workstations for software develop- ment and testing purposes, (2) IT centers to con- solidate dedicated servers onto more cost effective hardware, and (3) hosting organizations to cost ef- fectively sell virtual private servers at scale. These real-world scenarios have similar require- ments in terms of isolation between VMs—it needs to be strong. However, they differ substantially in their need for scalability, performance and the abil- ity to support multiple operating system environ- ments. For example, programmers or testers are unlikely to run a number of heavily loaded VMs concurrently, and while they would prefer good per- formance, their tolerance for poor performance is likely to be high. On the other hand, they are likely to depend heavily on the ability to support mulitple operating system environments. In fact, the abil- ity to run multiple software development and testing environments on the same hardware is the primary 2
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advantage of VM technlogy in this scenario. As another example, IT centers tend to consoli- date on the order of a dozen physical servers into VMs running on a more cost effective system. They rely on the ability to run multiple VMs concurrently (one per service), but in many environments, the load on each service may be relatively light. For example, a small company may maintain their web server, mail server, DNS server, and ftp server all on one physical machine. By placing each service in its own VM, they can limit the impact of a soft- ware failure to one service and also simplify the ad- ministration of each service. In this scenario, there would be little benefit to sharing due to the user- level server software, but it is likely that multiple services would run on the same operating sytem. In a third scenario, organizations selling virtual private servers at scale (e.g., web hosting compa- nies, Akamai, PlanetLab, and so on.) likely have many copies of the same server software and un- derlying operating systems represented in their mix of VMs. They seek to benefit from an economy of scale and need to reduce the marginal cost per customer VM. Thus they are likely to be extremely sensitive to issues of scalability and performance as they try to carefully oversubscribing their physical infrastructure with as many VMs as possible with- out reducing overall quality of service.
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  • Spring '12
  • GwangS.Jung
  • virtual machine, VMs, Linux kernel, Xen, namespace isolation

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