Virtualization. Innovation or Renaissance. Matthieu-P. Schapranow

Transcription

1 Virtualization Innovation or Renaissance Matthieu-P. Schapranow Hasso-Plattner-Institute for IT Systems Engineering University of Potsdam, Prof.-Dr.-Helmert-Str. 2-3, D Potsdam, Germany, Abstract. Is virtualization an innovation or does it experience a Renaissance? This question builds the basis for the given paper. The current hype around virtualization as solution for all resource and performance problems equals the introduction of a panacea. The given paper revises some of the business buzzwords and points out where virtualization is originated. Available virtualization products especially for mainstream computers such as x86 and x64 architectures are stated, their approaches and benefits for the nowadays IT landscape are outlined, compared and evaluated. Key words: Hypervisor, Platform Virtualization, Resource Virtualization, Network Virtualization, Server Virtualization, Storage Virtualization, Virtual Machine A paper in association with the Industrial Seminar in winter term 2006 by Prof. Dr. Andreas Polze, March 13th, 2007

2 Table of Contents Virtualization... 1 Matthieu-P. Schapranow 1 Introduction ComputationalPowerandCosts ComputationalAbstraction Virtualization ParadigmorProduct PlatformVirtualization ResourceVirtualization VirtualizationServices ServerVirtualization StorageVirtualization NetworkVirtualization VirtualizationProducts VMware... 7 VMwareserversolutions MicrosoftVirtualization... 8 MicrosoftVirtualPC... 9 MicrosoftVirtualServer Xen Conclusions List of Figures 1 Serverloadduring aworkingday Hypervisorarchitectures... 6

3 Virtualization Innovation or Renaissance 3 1 Introduction 1.1 Computational Power and Costs The available computational power increased rapidly during the last years, e.g. the CPU frequency increased by the factor 40 from 100 MHz up to four GHz. Additionally, the number of transistors per square exploded accordingly to Moore s Law. The Pentium 100 based on approximately 3.3 millions Transistors, the Pentium-IV consists of approximately 178 millions Transistors. That is an increase by more than the factor 50. With the increasing computational power the energy consumption and the amount of lost heat respectively energy gets more and more important. Especially large computer cluster suffer from this arising cost factor. World s largest search engine Google builds its business on commodity computers. In [1] their power problem is stated as "...a power density of 400 W ft. With higher-end processors, 2 the power density of a rack can exceed 700 W ft." The power density of a typical commercial data centers is up to a 2 factor ten lower, it varies between 70 and 150 W ft. 2 Furthermore, Barrosso et al. mention that the considered rack consisting of only 40 80x86 based computers consumes including cooling overhead approximately 10 MWh per month. That incredible amount of energy has to be produced on costs of the environment. A large amount of energy is already used by the running system on fixed rate independently of its load. 1.2 Computational Abstraction The Google example gives an overview of nowadays system s landscape. With the increasing variety of available hardware components the system architectures are interfused and become heterogeneous. However, system applications focus more and more on a small number of destination platforms to keep development costs low. The complexity of managing different system architectures on either both sides hardware and application side is a complex job. This counter-rotated development makes the virtualization paradigm an aged new-comer on the IT market. 2 Virtualization Paradigm or Product If complexity exceeds the imagination border people tend to introduce new levels of abstraction to handle the problem. Often real-life parallels are used to make the complex problem understandable. The virtualization paradigm has been introduced to separate two interacting components from each other. This is only a rough description of virtualization as it is a major paradigm that forms differently depending on its application area. In the following sections a choice of virtualization application is described and characterized to give examples where virtualization may be applied. 2.1 Platform Virtualization The term platform virtualization summarizes any method with the aim to offer multiple instances of a system often realized by software simulation. The virtual machine (VM) approach is one example for this virtualization category. Creasy gives in [2] a clear definition of a VM: "It provides a private, secure, and reliable computing environment for its users, distinct

4 4 Matthieu-P. Schapranow and isolated like today s [1981] personal computer." During the batchjob period in the 1960s the problem of system utilization occurred exactly as today. The VM idea was born on the basis of the existing Compatible Time- Sharing System (CTSS). As described in [2] IBM used this approach to test new hardware developments for Systems 370 on Systems 360 and to offer compatibility at the cost of speed. The VM approach is often used to virtualize only a part of the full available system to offer a subset of functionality for applications running in them. A complete simulation of the underlying hardware is cost-intensive and it does often only work with a defined subset of hard- and software. The full virtualization approach offers the most security and flexibility per VM. Products such as VMware Workstation, VMware Server, and Parallels Desktop offer almost full virtualization. They are available as COTS software for home and office use. The aforementioned CTSS and a lot of widely used operating systems (OS) for home and office such as Mac OS, Linux, and Microsoft Windows do not try to meet the full virtualization criteria. However, they are part of another category of virtualization products which allow partial virtualization. This is implemented on per-user and on per-process basis using the virtual memory approach 1. This virtual memory concept also goes back to the pioneers of the 1960s and was one tremendous innovative in computer science. The virtualization on OS level was introduced by thinking the VMS approach one step further. Applications running within the VM use the main parts of the hosting OS such as kernel and mandatory system libraries. This approach is widely adapted in the shared hosting business for web servers using products like Virtuozzo or Solaris Containers. Application-level virtualization also exists offering only a very small subset of functionality to run special software.thisisadequatetoofferspecialized solutions such as the Java VM to run Java byte code independently from the surrounding OS. This approach is also used for the Linux chroot command or by the User Account Control in Microsoft Windows Vista. 2.2 Resource Virtualization Based on the experiences of platform virtualization and grid computing the idea of resource virtualization was developed. The key concept is to extend the virtualization idea to almost any kind of resource such as storage virtualization using storage area networks, network virtualization using VLANs, processor virtualization by simulating one super computer consisting of multiple physical CPUs as mentioned in [4]. In this context virtualization can be interpreted as the process of mapping virtual resources onto physical resources. Virtual resources appear transparent to the consumer and may consist of partitioned or spanned physical resources. The according physical resources may be located centralized or distributed or even both. This virtualization approach offers a very flexible possibility to respond to fluctuating service demands. With the 1 "With virtual memory, memory space no longer had to be in the system s internal memory all at once." taken from [3]

5 Virtualization Innovation or Renaissance 5 hype of service-oriented architectures (SOA) this category of virtualization technique becomes more and more important. Service utilization is often unpredictable and especially if the variance between mean service utilization and peak utilization is high the resource acquisition is complex. Application Scenario Consider an online shop for electronic components which has typical utilization peak during day time as shown in figure 1 on the following page. In this scenario the resources are cumulative web servers and database servers. The mean utilization is about 64 percent and from 11 PM to 9 AM and around 8 PM the load is below this level. The minimal utilization is 16 percent and the maximal utilization is about 155 percent. On the one hand, the expensive alternative is to meet peak utilization of 155 percent, but accepting long periods with resource idle times, i.e. 23 of 24 hours. On the other hand, you may acquire resources regarding the mean utilization with the drawback that some consumers will not be able to use the service during peak times, i.e. twelve of 24 hours. Obviously both alternatives are inadequate. The optimal compromise is to acquire resources accordingly to the lowest permanent utilization of 16 percent utilization and adding additional resources on demand. This scenario exemplarily indicates a very common problem in client server scenarios. If applications are bound to real physical resources the scalability of the service performance is relatively bad. The step-wise improvement of performance can only be achieved by adding an additional server offering the same service, implementing a load balancing technique and in case of database system ensuring the consistency of distributed database data. That involves a high technical and personal involvement and affects total costs of ownership (TCO) drastically. 3 Virtualization Services With the help of the virtualization classification as described in section 2 on page 3 the following section illuminates selected virtualization methods for industrial services and products. The selected categories of virtualization are basic building blocks for industrial services and products. It is possible to provide virtualization based on one of the following categories as well as on their combination or even on all categories for virtualization. For instances, for the company Sun virtualization is the base of their Datacenter Grid strategy which builds on the orchestration of network, storage, server virtualization and the provided business services to provide one homogenous platform. Obviously, there is a need for agility in IT landscapes which will result in a decoupling of software and hardware infrastructure. 3.1 Server Virtualization The server virtualization belongs to the category of platform virtualization as described in section 2.1 on page 3. Three approaches exist to reach the aim of a partitioning. The virtual machine approach offers each guest OS within the VM a clean and unique environment. All offered hardware resources appear to be dedicated for the current guest OS while the host OS is completely hidden from

6 6 Matthieu-P. Schapranow Fig. 1. Server load during a working day Virtual System 1 User Applications Virtual System n User Applications Paravirtual System User Applications Unmodified Operating System Unmodified Operating System Extended Operating System Virtual Hardware Resources Virtual Hardware Resources Virtual Hardware Resources Transparent Hypervisor Physical Hardware Fig. 2. Hypervisor architectures

7 Virtualization Innovation or Renaissance 7 the guests. However, if the guest OS tries to allocate real physical hardware resources, such as memory storage, all system calls are tunneled through a hypervisor also called virtual machine monitor (VMM). A hypervisor coordinates and manages the access of multiple guest OS to physical resources acting as a host component as shown on the left side of figure 2 on the preceding page. The paravirtual machine (PVM) model acts similar to the VM approach. Products implementing this PVM model manipulate the code of the guest OS to reduce the amount of system calls by offering interfaces between guest OS and hypervisor as shown on the right side of figure 2 on the facing page. Thus, it is possible to reduce the virtualization overhead and additional host OS resources can be made available by using a hypervisor. This model is implemented by products of XEN and UML as described in section 4.3 on page 10. OS-level virtualization exposes kernel functionality of the hosting system to the guest systems. The guest OS may run its unmodified programs and is able to access almost all hardware components. These programs have to be built using the system libraries and kernel version installed on the host OS. This model is widely used in shared hosting environments for web servers. Products like Solaris Zones and Virtuozzo implement this model. 3.2 Storage Virtualization Storage Virtualization is the approach of centralizing the administration of multiple storages to a single storage appearing homogenously. So it is possible to plan centralized backups and maintenance jobs. This storage may be partitioned to meet individual requirements. So-called storage area networks (SAN) can be built by virtualization software or with hardware support. Nowadays even personal computers offer integrated hardware RAID controllers which are able to handle multiple physical hard disk drives to be spanned (RAID-0) or mirrored for performance and redundancy (RAID-1) or even both (RAID-5). 3.3 Network Virtualization Network Virtualization splits the available network capacity in virtual channels which can be assigned on perresource basis. This can be done for security reason to separate different services or quality levels from each other. Additionally, this is a mandatory feature to provide migration of running virtual machines between physical or logical location without downtime. 4 Virtualization Products In the following section a selection of major products in the COTS market for virtualization products is described. The presented subset of possible products is already used by 3rd parties to provide integrated virtualization solutions. For instances, SAP provides the SAP Dynamic Capacity Management to offer better hardware utilization and maintenance control for business solutions based on VMware products. 4.1 VMware VMware offers a diversified product portfolio for home/office and for

8 8 Matthieu-P. Schapranow server/datacenter use. In the following section only a selected server product is described for comparison purposes. VMware server solutions VMware offers virtualization products for the huge market of general purpose x86 architecture computers. The VMware products derive their names from the initial approach of using a virtual machine for virtualization. The VMware ESX Server solution as described in [5] consists of a hypervisor which manages access to physical hardware as described in section 3.1 on the preceding page. Figure 2 on page 6 shows the hypervisor layer directly attached to the physical hardware without any host operating systems. The hypervisor may run as transparent hypervisor hosting traditional virtual machines or as active actor to support extended OS in the virtualization environment. VMotion offers migration of running virtual machines between logical systems and is part of the VMware Infrastructure. This offers the possibility to migrate running services to faster physical or logical systems without downtime accordingly to their demand. Consider the example in section 2.2 on page 5 where the systems suffer from ahighuserratefrom10amto5pm. VMotion is able to move the complete running instance of an application to a more powerful server system for these operation hours and move it back when system load decreases. Asdescribedin[6]themaindata storage of the VM is hosted centrally on SAN using the specific Virtual Machine File System (VMFS) which offers concurrent access from different physical locations. After initiating the move the content of the VM s RAM is transferred via high speed network channels to the destination system. Meanwhile, the delta of changes done in the RAM of the source VM is synchronized in real-time until a heuristic algorithm determines the time to stop the source VM. Then it copies the remaining delta of data to the destination system and resumes the suspended system on the destination system. Finally, the virtual network identity is transferred from the source VM to the destination VM to accept all incoming network connections for the prior VM. The final switching takes only a few milliseconds which results in a constant data flow and uninterrupted network connections. The whole migration process appears to be transparent to the system user without any influence on the current work. Distributed Resource Scheduler (DRS) is build on the VMotion functionality and offers automatic resource allocation. Using the VMotion approach the system allocation has to be triggered by an observing administrator. With the help of the DRS adaptive resource allocation, i.e. system allocation, is chosen based on pre-defined rules. As described in [7] this offers more flexibility on the IT scalability factor, because new hardware can be integrated in the resource pool and will be assigned automatically based on business priorities. This may result in a reduce of maintenance costs and guarantees a balanced utilization across existing hardware resources. 4.2 Microsoft Virtualization The virtualization product portfolio of Microsoft was established 2003 when

9 Virtualization Innovation or Renaissance 9 the company Connectix and their product Virtual PC was integrated in the product strategy. In the next section Microsoft s current Virtual PC implementation for home and office use is described and their product announcements for the server and datacenter market are mentioned. Microsoft Virtual PC Microsoft Virtual PC 2007 runs on host systems starting from Windows XP and newer. Thus, it depends on an installed Windows environment and makes use of the VM approach as mentioned in section 3.1 on page 5. The current version comes with some limitations. The set of full supported guest OS is limited to Windows Vista Enterprise, Windows Vista Business, Windows Vista Ultimate, Windows 98, Windows Me, Windows 2000 Professional, Windows XP, OS/2. It is also possible to install UNIX or Linux derivatives but they are not supported. The emulation of physical hardware underlies limitations: USB devices using non-integrated Windows drivers are not supported. Additionally, the physical installed graphic card is not virtualized, instead a generic device is emulated. So you cannot use specific drivers for your graphic card s hardware, currently. SCSI devices of any kind are also unsupported. In all VMs the following hardware components are emulated as software components: the buses, DMA controller, keyboard controller, IDE/ATA controller, interrupt controller, I/O controller, memory controller, NVRAM, power-management hardware, programmable timers, and real-time clock. Virtual Hard Disks (VHD) describes different types of virtual devices which are supported by MS Virtual PC : Dynamically Expandable VHDs are physically stored in a single file on the host system consuming very small storage initially and growing with the data size used in the VM. Fixed-Size VHDs appear in the same way as Dynamically Expandable VHDs do, but its size does not adapt, it is created initially and does neither grow nor shrink. Linked VHDs are used to virtualize a complete physical hard disk drive, thus Linked VHDs are mapped to a physical pendant. In addition all aforementioned VHD types can make use of the following features. The first one is the differencing VHDs feature which offers the possibility to use centralized VM image templates for multiple running instances, concurrently. Changes made on per VM basis are maintained on an individual differencing VHD. The second feature is called undo disk which offers the user the possibility to reward all changes done between VM start and shutdown. This feature can be used to test software each time under the same development conditions regardless on the changed done during the last run. Microsoft Virtual Server Microsoft extends its product portfolio and announced its new solutions in Microsoft plans to provide complete solutions for virtual datacenter such as the Microsoft System Center Virtual Machine Manager. In combination with the new MS Longhorn OS a hypervisor-based virtualization solution has been announced as mentioned in [8]. Especially the MS

10 10 Matthieu-P. Schapranow Longhorn Server OS contains specific modifications to optimize work in a hypervisor-based environment with Microsoft virtualization products: "...[it] has been developed to take advantage of hypervisor-based virtualization. This is Windows Server virtualization." (taken from [8]). 4.3 Xen Xen is another competitor on the huge market of virtualization products which is driven by their open source community. The product portfolio consists of three major versions: XenServer, XenEnterprise, and Xen- Express which address business users, datacenter providers, and home/office users. In combination with the Microsoft attempt of hypervisor virtualization Xen is part of a relationship with MS and supports Microsoft s virtualization strategy. The main driver of their architecture is their open source hypervisor. In contrast to other hypervisors this product has been developed in cooperation with hundreds of developers from different companies such as IBM,HP,Intel,andAMD. In combination with their hypervisor architecture Xen introduced their hypercall API which enables guest OS to interface with the hypervisor directly. One resulting major advantage is the reusability of software drivers for the real hardware, as they may interface directly through the hypercall API. New CPU generations such as the AMD s AMD-V architecture and the Intel s VT system may support virtualization in a completely new way. This hardware support is a result of the cooperation between Xen developers and hardware vendors. 5 Conclusions As described in section 4 on page 7 a lot of virtualization products based on the hypervisor approach exist. However, there are different ways to integrate the hypervisor idea. On the one hand, the host resources such as hardware devices and memory are completely emulated to the guest OS. Any attempt to execute privileged access to the virtual resources is handled by the surrounding VM which then interacts with the physical resources on behalf of the guest OS. This approach is called the ring deprivileged approach. Some CPU architectures make it necessary to modify the desired operation codes before executed on the physical hardware. This binary patching approach is done by observing and patching instructions on the fly. On the other hand, the paravirtualization approach is widely in use. This approach replaces the need for patching instructions on the fly with the need of collaboration by the OS vendors. Their products must support hypervisor-specific virtualization hooks to interface directly with the hypervisor. The use of these hooks results in performance and security increase. Hardware vendors already started to integrate technical enhancements to support direct hypervisor technology as mentioned in section 4.3. This may tremendous improve the performance for virtualized guest OS. Additionally, the major part of OS vendors agreed to support hypervisor functionality in their kernels with the upcoming version for x86 and x64 OS asdescribedin[9]. These two efforts show up that both hardware and software vendors

11 Virtualization Innovation or Renaissance 11 are committed to support virtualization in production mode. The re-arisen hype for virtualization may become more interesting in words of reduced maintenance costs, minimal licenses for software products on per host basis, better utilization of existing and future hardware resources. Existing virtualization approaches from the last decades are kept almost unvaried. Nevertheless, the implementations have been optimized. This is a result of the convergence of hardware vendors and software vendors in this development area. The virtualization hype profits from developments of the grid computing research. For instances, process allocation or process migration is adapted for virtual IT landscapes. The presented virtualization trends arise from a cost-reducing attempt. Comparing to the late 1960s as referred to in section 2.1 on page 3 the development driver was the same. Nowadays, the aim of server systems is providing services. Especially in SOAs it becomes more and more important to guarantee response times and reliability for provided services. If application decoupling and mixture of used services keeps on increasing the application developer loses influence for response times and functionality of the orchestrated services. Ultimately, the usage of virtualization for IT landscape will increase tremendously regardless of the improvements in physical performance increases. This is supported by the fact that the process of enabling a physical system for virtualization becomes simpler, even mainstream x86 and x64 computer architectures are supported as described in section 4 on page 7. Additionally, virtualization software already becomes a pendant to database software which has become an essential part of the infrastructure. It does not even require high monetary invests. This will dramatically support the acceptance process for virtualization in the next few years. References 1. Barroso, L.A., Dean, J., Hölzle, U.: Web Search for a Planet: The Google Cluster Architecture. IEEE Micro (2003) 2. Creasy, R.J.: The origin of the VM/370 Time-Sharing System. IBM Journal of Research and Development 25(5) (1981) 3. Rainville, J., Howard, K., Peck, K.: OpenVMS at 20 Nothing Stops it. Digital Equipment Corporation (1997) 4. Figueiredo, R., Dinda, P.A., Fortes, J.: Resource Virtualization Renaissance. IEEE Computer Society (2005) 5. VMware: VMware ESX Server Platform for virtualizing servers, storage and networking. vmware.com/pdf/esx_datasheet.pdf (2006) 6. VMware Global Inc.: VMware VMotion Live migration of virtual machines without service interruption. vmotion_datasheet.pdf (2006) 7. VMware Global Inc.: VMware DRS Dynamic balancing and allocation of resources for virtual machines. datasheet.pdf (2006) 8. Gates, Bill: Advancing the Platform. presspass/exec/billg/speeches/ 2006/05-23WinHEC.mspx (2006) 9. XenSource Inc.: Introducing the XenServer Product Family A XenSource White Paper. xensource.com/files/xenserver_ whitepaper.pdf (2006)