Clearly better virtualization with Citrix XenServer. White paper

Transcription

1 White paper Clearly better virtualization with Citrix XenServer Citrix XenApp customers can achieve server consolidation, faster server deployment, improved application availability, and easier management by virtualizing their servers using Citrix XenServer.

2 Table of contents Summary Brief overview of the virtualization stack... 3 Application virtualization challenges... 4 The case for virtualizing Citrix XenApp with Citrix XenServer... 5 Virtualization scenarios... 6 Consolidation... 7 Simplified management... 8 Application availability... 9 Conclusion

3 Summary IT organizations successfully deploy virtualization every day to maximize utilization of existing computing resources and more quickly provision systems, services, applications and desktops. Virtualization helps reduce datacenter operating expenses and increases the availability of critical business systems. The result is an IT organization with greater agility and a new ability to address even the most complex business imperatives. However, many IT teams cling to the outdated notion that it is not advisable to deploy application and server virtualization technology together. This paper shows that server and application virtualization are complementary and how they can and often should be combined, not only to amplify the capabilities of the respective technologies but to achieve greater positive impact to IT and the business. More importantly, this paper will help IT managers navigate the complex stack of virtualization technologies and prescribe some pragmatic methods to combine server and application virtualization together to deliver a more dynamic, agile and cost-effective IT infrastructure. Brief overview of the virtualization stack In its most fundamental form, virtualization is the decoupling of logical computing resources from physical hardware. This is not a new concept; in fact, virtualization has pervaded information technology in many different forms over the past few decades, including server, workstation, desktop, application, storage and I/O virtualization. The focus of this paper is on two of these virtualization technologies: server and application virtualization. Server virtualization enables one physical server to support multiple workloads in simultaneously running virtual machines. The workload consisting of an operating system, application set and configuration is decoupled from the physical computing platform by means of a virtual machine. This achieves some important things, such as isolation (running multiple workloads safely and securely on a single computing platform) and workload portability (moving the workload across different physical computing platforms). It is even possible with more advanced server virtualization platforms to migrate actively running workloads across physical servers. This allows the workload to float across a pool of physical computing resources, enabling IT departments to maximize available computing resources, reduce costs and deliver applications to users reliably and effectively. Figure 1: Citrix XenServer server virtualization improves server utilization and helps deliver applications more efficiently by streaming server workloads. 3

4 Citrix XenServer is server virtualization and dynamic workload delivery management software that includes all the important elements of virtualization, including centralized lifecycle and workload management, storage, live migration, high availability and real-time streaming. It improves server utilization, lowers costs and simplifies server administration and deployment of applications across physical and virtual environments. The foundation of Citrix XenServer is the open source Xen hypervisor, a proven reference standard for server virtualization. The Xen hypervisor is implemented as an extremely thin layer of software which resides between the bare metal hardware and the virtualized operating systems. The hypervisor provides the all-important abstraction layer that allows each physical server to run one or more virtual servers, effectively decoupling the operating system and its applications from the underlying physical resource. To achieve the greatest degree of virtualization performance and security, the Xen hypervisor uniquely utilizes two techniques: paravirtualization and hardware-assisted virtualization. These techniques are widely acknowledged as being the most scalable, robust and secure forms of virtualization. For the IT organization, the Xen approach to virtualization translates to minimal overhead and near-native performance for virtualized workloads. Application virtualization is a technique for isolating an application from the underlying system. With application virtualization, the applications may run in isolation directly on the user s desktop system, or remotely on a server with the application interface displayed on the user s desktop, regardless of the underlying platform or operating system. Citrix XenApp is a Windows application delivery system that manages and virtualizes all applications in the datacenter for optimal application performance and flexible delivery. With it, you can deliver all Windows applications to office, task and mobile users on demand, either run centrally from the datacenter or streamed down to the user s preferred device. A single copy of the application is managed centrally, reducing support and maintenance costs by as much as 40 percent. With more than 100 million users and 99 percent of the Fortune global 500 as customers, XenApp is the leader in delivering Windows-based applications with the best performance, security and cost savings. Application virtualization challenges At the same time as Citrix XenApp server deployments have grown in scale and scope across the enterprise, complex, new infrastructure challenges have arisen. This complexity can be attributed to a number of factors, such as the need to support new applications while continuing support of existing ones or challenges in scaling the XenApp server infrastructure within a static datacenter. At the same time, disruptive technological shifts, such as the transition from 32- to 64-bit computing platforms, have introduced more complexity into XenApp environments. While many XenApp customers are eager to migrate to 64-bit platforms in order to take advantage of greater memory limits and higher user densities per server, the problem of supporting old legacy applications remains a gating factor. Many of these legacy applications are either not supported by or are actually incompatible with 64-bit platforms. As a result, silos of low-density 32-bit XenApp servers must be maintained as the rest of the environment transitions to 64-bit, resulting in more complexity combined with greater management overhead. Another area of complexity has been the support of multiple geographically distributed XenApp server deployments. These servers may reside in headquarters or branch offices and be designated to serve distinct populations of IT consumers. The management complexity and consistency challenges and entrenched silo mentality have yielded a proliferation of XenApp servers across the 4

5 enterprise. More urgently, as the number of XenApp servers has increased, the costs associated with powering, cooling, housing and managing all those servers across all those branch offices continue to strain IT budgets. Although XenApp application virtualization has proven itself effective in accelerating delivery of new applications, there are still scaling challenges in the datacenter to ensure that the requisite computing and storage infrastructure supports the new applications. An example of this is an initiative to minimize the time associated with XenApp server change management, especially as changes need to proliferate across development, test and production environments. Similarly, IT is looking for better strategies to provision XenApp servers more rapidly, consistently and economically with fewer resources. Finally, the uptime and availability of applications remains a primary concern for all IT organizations. Financial impact to the organization due to both planned and unplanned hardware maintenance can be easily quantified in XenApp environments. The impact of downtime is especially painful where the delivery of applications is governed by strict service level agreements or the cost of application downtime can be easily monetized, such as in retail environments. While XenApp technologies like zone preference and failover help ensure the reliability of the application sessions and the routing of users in the event of site failures, the uptime provided by an individual XenApp server is still inexorably linked to the uptime of the underlying hardware. In other words, if a server or component fails or a server needs to be powered down for hardware maintenance while applications are running, all user application sessions on that server will be disrupted. The case for virtualizing Citrix XenApp with Citrix XenServer While the benefits of application virtualization with Citrix XenApp are clear, IT organizations are now looking to utilize their resources more effectively, enhance application availability, and realize additional return on the investment in XenApp through server virtualization. Yet, while many IT organizations value the consolidation, management and availability benefits of server virtualization for their XenApp environment, there are still concerns about the overhead that virtualization will impart on the application delivery infrastructure. Early generation virtualization platforms notoriously caused severe drops in XenApp server scalability sometimes as much as 50-60% degradation in the number of concurrent users that a single virtualized instance of XenApp could support compared to running XenApp natively on a single physical server. As a result, some organizations are reluctant to engage in any discussion about virtualizing XenApp servers. Fortunately, Citrix XenServer has been performance-optimized for XenApp workloads. Introduced in XenServer 4.1, the XenApp server template allows XenServer administrators to easily configure performance-optimized virtualization for their XenApp server deployments. Optimizing XenServer for XenApp is surprisingly easy. Administrators simply need to create a new virtual machine using XenServer s built-in App template. That s it! How significant are these performance optimizations? More specifically, what is the quantifiable impact of the server virtualization overhead on a typical XenApp server deployment? Recently, The Tolly Group, an independent analyst firm, published a scalability benchmark of 64-bit XenApp 4.5 Feature Release 1 when virtualized on XenServer 4.1. According to their report, the XenApp template in XenServer introduced a virtualization overhead of just 7.6% for 64-bit XenApp workloads. In other words, the degradation in the number of concurrent users that a single virtualized instance of XenApp could support was only 7.6% 287 concurrent users per server, compared to the same XenApp instance running on a comparable physical server at 310 users. Furthermore, internal testing by Citrix showed that in certain deployment scenarios XenServer 4.1 could support up to 70% more concurrent users per virtualized XenApp server than one of Citrix s leading server virtualization competitors could support. 5

6 Considering the levels of performance degradation that are commonly found in the real world, achieving virtualization with less than 10% performance overhead, is an indication that Citrix has succeeded in tuning XenServer to virtualize XenApp workloads. The Tolly Group Performance Evaluation of XenApp in a 64-bit Virtualized Server Environment Using XenServer May 2008 Virtualization scenarios There are three main benefits that server virtualization with Citrix XenServer can bring to Citrix XenApp environments. First, server virtualization can provide significant benefits and cost-savings through server consolidation. By virtualizing and consolidating underutilized XenApp servers and application silos, the investment in existing IT resources can be maximized while simultaneously reducing server footprint in the datacenter and achieving a far greater degree of server utilization. Additionally, the isolation and scalability benefits of a 64-bit virtualization platform can allow multiple 32-bit workloads to be consolidated on highercapacity, more cost-effective 64-bit servers. During internal testing, a three-year old server running Windows Server bit with XenApp 4.5 maxed out at fifty concurrent users, while a single 64-bit server easily ran four virtual machines (running Windows Server bit with XenApp 4.5) with fifty users each a total of 200 users across four virtual machines. The four virtualized XenApp workloads running on the 64-bit server delivered the same level of user performance delivered by XenApp on the three-year old physical server. The tests demonstrate that by buying new hardware and using XenServer to virtualize XenApp, server scalability can be quadrupled, power consumption can be reduced by 60% and physical server count can be cut by 75%. (Note that, given the efficiency gains in server platforms in the past few years, the hardware investment cost can often be more than offset in savings on power and cooling.) The tests demonstrate that by buying new hardware and using XenServer to virtualize XenApp, server scalability can be quadrupled, power consumption can be reduced by 60% and physical server count can be cut by 75%. Second, server virtualization and dynamic workload management with XenServer introduces a new and simplified management paradigm for XenApp environments. For example, it is now possible to manage and provision XenApp servers across both physical and virtual server infrastructure. This provides a new level of IT flexibility for testing, development, production and disaster recovery environments. This also allows IT to dynamically provision new XenApp servers as business demands dictate, such as at month-, quarter- or year-end when traffic to line-of-business applications tends to be the highest. And, since a single XenApp server image can be used to bootstrap both physical and virtual servers, it has become far easier to move XenApp servers between the physical infrastructure, such as what may be deployed in the primary datacenter, and the virtual infrastructure, such as in the disaster recovery site. 6

7 Third, XenServer adds a new solution to the IT repertoire to enhance the overall availability of XenApp applications. By virtualizing XenApp servers, it becomes possible to deliver applications to end-users with a far greater degree of uptime and resiliency. One of the ways that server virtualization can accomplish this is by effectively decoupling the uptime of the application from the underlying hardware using XenMotion, the live migration technology available with XenServer. Furthermore, features such as dynamic workload delivery can simplify disaster recovery strategies for XenApp environments, an especially critical capability in the event of total datacenter failure. Consolidation While many physical XenApp servers are already operating at high utilization rates and may not seem like good candidates for virtualization, there are several common scenarios where IT organizations can achieve meaningful consolidation of their XenApp servers with XenServer. For example, due to limitations in the memory architecture in the 32-bit editions of Windows Server 2003, 32-bit XenApp customers can quickly run into known scalability barriers which artificially govern user density on the server. This limitation is due to the Windows memory management architecture in which each application is constrained to its own virtual 4 GB memory space which is evenly divided into two parts 2 GB of memory dedicated for kernel usage and the remaining 2 GB dedicated for application usage. Although each application gets its own 2 GB of memory, all applications have to share the same 2 GB of kernel space. As users begin to load a XenApp server, the total number of user sessions that can be supported by the server ends up being constrained by the shared kernel memory limits. One opportunity for consolidation is virtualizing silos of 32-bit XenApp servers and consolidating them on 64-bit servers running XenServer. Consolidation of 32-bit servers on a 64-bit virtualization platform allows the XenApp administrator to break through the 4 GB memory barrier imposed by 32-bit platforms, an especially important benefit for environments with memory-bound applications. 64-bit virtualization also allows XenApp servers to be scaled horizontally. In other words, by moving to multiple instances of 32-bit XenApp virtual machines on a single 64-bit server platform, XenApp customers can effectively increase their XenApp user density per physical server, especially with new 64-bit x86 servers shipping from the factory with 32, 64, or even 128 GB of RAM pre-installed. Finally, for organizations that are not ready to migrate off their legacy 32-bit applications but are highly motivated to replace their depreciated and outdated 32-bit servers, XenServer virtualization allows them to conveniently leverage the capacity of 64-bit servers without dictating an expensive and complex upgrade for the underlying applications. Figure 2: XenServer can be used to consolidate multiple existing 32-bit XenApp workloads on a single physical 64-bit server. 7

8 Similarly, many XenApp customers also discover that they can consolidate underutilized XenApp support and infrastructure servers, such as the licensing server, SmartAuditor server or Web Interface. In many XenApp deployments, there may be the need for a specific, standalone component and these standalone servers may rarely, if ever, be highly utilized. As a result, lightly-utilized support and infrastructure servers often make excellent candidates for virtualization, allowing the XenApp administrator to achieve consolidation without noticeably impacting end-user experience or application performance. Virtualization with XenServer also allows XenApp administrators to isolate and consolidate rarely utilized application silos as unique virtual machines running on a single host server. The savings in power, cooling and real estate achieved by virtualization can be quite significant. Finally, by consolidating XenApp server farms, IT organizations can realize a meaningful reduction in server operating costs. Since much of the cost associated with operating a server is due to power and cooling consumption, organizations can now green their IT operations and ultimately contribute to the consumption of fewer natural resources. These aptly-named green IT initiatives allow businesses to achieve significant cost savings through lower utility bills, become a pillar of environmentally progressive corporate social responsibility programs and, in some jurisdictions, realize government tax incentives. Simplified management XenServer has taken a unique approach to ensure simple, powerful, centralized manageability. At its core, XenServer provides bare-metal server virtualization allowing multiple virtual machines to run on a single physical server without the need for a heavyweight operating system. This bare-metal approach to virtualization differs significantly from earlier generation hosted virtualization offerings in which virtualization software ran atop a general-purpose operating system. This had a number of disadvantages, including severe degradations in performance and scalability, and the introduction of additional management overhead for the underlying host operating system. XenServer management is simple and efficient. There is no underlying host operating system to manage; the virtual machines can be managed entirely within the easy-to-use and remarkably lightweight XenCenter management console. The XenCenter console can even be made available as a published XenApp application. XenServer also helps provide greater flexibility in XenApp environments by allowing application workloads to be streamed to either physical or virtual infrastructure from a single virtual disk (or golden image). This makes it far easier to maintain, manage, update and patch XenApp servers as well as ensure consistent process regardless of whether physical or virtual infrastructure is utilized. These capabilities enable XenApp workloads to be delivered on-demand rather than be physically installed on top of individual servers. XenServer allows an administrator to create a virtual image of any XenApp workload and stream it from network storage to either physical or virtual servers. These target servers do not even need to have internal storage and, more remarkably, can be bootstrapped from a single workload image stored on the network. In some scenarios, up to 1,000 servers, physical or virtual, can be booted from the same golden image leading to dramatic reductions in storage usage, especially for large XenApp server deployments translating into significant cost savings. Dynamic workload management also allows IT organizations to switch between physical and virtual XenApp deployments quickly and easily as business conditions dictate. For example, consider a scenario in which seasonal staff increases put tremendous pressure on IT staff to scale out XenApp application delivery capacity. XenServer can help provision new XenApp servers dynamically, allowing IT staff to rapidly scale up to meet application demands, and to scale down when demand diminishes. 8

9 Figure 3: Dynamically streaming workloads to physical and virtual machines reduces the storage and administration requirements for application delivery. Furthermore, with so many complex and multi-tiered XenApp deployments, many customers are looking for greater flexibility when managing development, test and production environments. For example, trying to keep a XenApp test environment in sync with a production environment, let alone expending the resources to fully replicate each environment, is an arduous task. This is compounded by the fact that test environments are not the main focus of the business they are temporary and discarded once they have served their purpose. Rather, the core focus of IT is centered on the production environment with the most stringent service level agreements and highest end-user expectations. It is this very practical contradiction which causes XenApp testing and production environments to fall out of sync, thus making it more complicated, time-consuming and expensive to deliver new applications. In many cases, IT organizations may opt to deploy XenApp on virtual infrastructure in their test environments to ensure maximum utilization of limited physical resources, but standardize on physical infrastructure in production environments for greatest possible performance or third-party ISV support. The fact that XenServer can provision XenApp workloads agnostically to physical and virtual infrastructure means that it is not necessary to assign rigid roles to individual servers. Application availability Some of the more recent technological innovations in server virtualization such as workload management, high availability, and live migration have transformed virtualized servers into a more flexible, resilient and highly available infrastructure compared to their physical predecessors. These capabilities are finding new uses to help businesses achieve a more agile and responsive IT infrastructure and solve disaster recovery and application availability challenges. In traditional XenApp server deployments, application workloads run directly on bare-metal servers. While this can ensure the best possible application performance, it also means that hardware maintenance events impact application uptime and availability. For example, in the event IT needs to replace a hardware module in a server, they must typically schedule a maintenance window to power down servers to replace the faulty or outdated component. During this window, the applications and user sessions running on that server are interrupted, thus disrupting availability of the application. The live migration feature of XenServer, called XenMotion, enables IT organizations to decouple hardware maintenance events from application uptime by making virtualized application workloads portable across physical servers. With XenMotion, actively-running virtual machines can be migrated from one physical server to another with no application interruption. This allows critical XenApp servers and applications to remain running even if an entire server needs to be taken down, enabling 9

10 zero-downtime maintenance. Live migrations of XenApp virtual servers are seamless: they can be initiated via a simple drag-and-drop operation or command and do not impact the end-user or the running applications. Figure 4: XenServer can migrate active XenApp workloads to alternate physical machines without any downtime. XenServer also offers built-in high availability for virtual machines as well as third-party options for fully continuous fault tolerant operation. With high availability, virtual machines and their associated workloads can be restarted automatically on another physical host in the event that the original host fails. This provides the IT administrator with peace of mind that in the event of a physical host failure, application workloads will automatically restart with no requirement for human intervention. Fault-tolerance extends the concept of high availability by adding an even higher degree of resiliency and proactive protection against component and system-level failures. Fault tolerance can protect applications continuously and ensure zero application downtime or end-user disruption even in the event of hardware failures. Fault tolerance for XenServer virtualization is the most cost-effective way to introduce the highest degree of application resiliency for your most mission-critical XenApp deployments. Finally, XenServer can help organizations streamline their approach to disaster recovery of XenApp server deployments by giving IT the ability to rapidly transfer their XenApp workloads and applications from a primary datacenter to a disaster recovery (DR) site as part of a simple business process. By leveraging the power of dynamic workload management and virtualization, IT organizations can shift applications from one site to another in a few minutes using a fraction of the physical infrastructure at the DR site. Conclusion While the benefits of server virtualization in early generation products were often offset by performance and complexity tradeoffs, only a Citrix XenServer solution makes virtualization simple and economically feasible for Citrix XenApp environments and other key infrastructure components. The use of XenServer can result in a consolidated infrastructure that enhances availability and continuity of applications while helping to optimize hardware capacity utilization without sacrificing the performance of critical business services. With Citrix XenServer and Citrix XenApp, IT can really do much more with less. Interested? To download a free 30-day trial copy of Citrix XenServer Enterprise Edition, visit 10

11 Citrix Worldwide Worldwide headquarters Citrix Systems, Inc. 851 West Cypress Creek Road Fort Lauderdale, FL USA T T Regional headquarters Americas Citrix Silicon Valley 4988 Great America Parkway Santa Clara, CA USA T Europe Citrix Systems International GmbH Rheinweg Schaffhausen Switzerland T Asia Pacific Citrix Systems Hong Kong Ltd. Suite 3201, 32nd Floor One International Finance Centre 1 Harbour View Street Central Hong Kong T Citrix Online division 6500 Hollister Avenue Goleta, CA USA T About Citrix Citrix Systems, Inc. (Nasdaq:CTXS) is the global leader and the most trusted name in application delivery infrastructure. More than 200,000 organizations worldwide rely on Citrix to deliver any application to users anywhere with the best performance, highest security and lowest cost. Citrix customers include 100% of the Fortune 100 companies and 99% of the Fortune Global 500, as well as hundreds of thousands of small businesses and prosumers. Citrix has approximately 6,200 channel and alliance partners in more than 100 countries. Annual revenue in 2007 was $1.4 billion Citrix Systems, Inc. All rights reserved. Citrix, Citrix XenApp, Citrix XenServer are trademarks of Citrix Systems, Inc. and/or one or more of its subsidiaries, and may be registered in the United States Patent and Trademark Office and in other countries. Microsoft and Windows are registered trademarks of Microsoft Corporation in the United States and/or other countries. UNIX is a registered trademark of The Open Group in the United States and other countries. All other trademarks and registered trademarks are property of their respective owners. 0808/PDF