citrix xenapp and citrix xenserver - better together

7/30/2019 Citrix XenApp and Citrix XenServer - Better Together

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White paper

Clearly better virtualization

with Citrix XenServer

Citrix XenApp customers can achieve server consolidation, aster

server deployment, improved application availability, and easier

management by virtualizing their servers using Citrix XenServer.


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Table o contentsSummary

Brie overview o the virtualization stack ......................................................................................... 3

Application virtualization challenges ............................................................................................... 4

The case or virtualizing Citrix XenApp with Citrix XenServer .......................................................... 5

Virtualization scenarios .................................................................................................................. 6

Consolidation ................................................................................................................................. 7

Simplied management ................................................................................................................. 8

Application availability .................................................................................................................... 9

Conclusion


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SummaryIT organizations successully deploy virtualization every day to maximize utilization o existing computing

resources and more quickly provision systems, services, applications and desktops. Virtualization helps

reduce datacenter operating expenses and increases the availability o 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 However, many IT teams cling to the outdated notion that it is not advisable to deploy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

oten should be combined, not only to ampliy the capabilities o 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 o virtualization technologies and prescribe some pragmatic methods to

combine server and application virtualization together to deliver a more dynamic, agile and cost-eective

IT inrastructure.

Brie overview o the virtualization stack

In its most undamental orm, virtualization is the decoupling o logical computing resources rom physical

hardware. This is not a new concept; in act, virtualization has pervaded inormation technology in many

dierent orms over the past ew decades, including server, workstation, desktop, application, storage

and I/O virtualization. The ocus o this paper is on two o these virtualization technologies: server and

application virtualization.

Server virtualization enables one physical server to support multiple workloads in simultaneously runningvirtual machines. The workload consisting o an operating system, application set and conguration

is decoupled rom the physical computing platorm by means o a virtual machine. This achieves some

important things, such as isolation (running multiple workloads saely and securely on a single computing

platorm) and workload portability (moving the workload across dierent physical computing platorms).

It is even possible with more advanced server virtualization platorms to migrate actively running workloads

across physical servers. This allows the workload to foat across a pool o physical computing resources,

enabling IT departments to maximize available computing resources, reduce costs and deliver applications

to users reliably and eectively.

Figure 1: Citrix XenServer server virtualization improves server utilization and helps deliver applications

more eciently by streaming server workloads.


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Citrix XenServer is server virtualization and dynamic workload delivery management sotware that

includes all the important elements o virtualization, including centralized liecycle and workloadmanagement, storage, live migration, high availability and real-time streaming. It improves server

utilization, lowers costs and simplies server administration and deployment o applications across

physical and virtual environments.

The oundation o Citrix XenServer is the open source Xen hypervisor, a proven reerence standard

or server virtualization. The Xen hypervisor is implemented as an extremely thin layer o sotware

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, eectively decoupling the operating system and its applications rom the underlying

physical resource. To achieve the greatest degree o virtualization perormance 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 orms

o virtualization. For the IT organization, the Xen approach to virtualization translates to minimal

overhead and near-native perormance or virtualized workloads.

Application virtualization is a technique or isolating an application rom the underlying system. With

application virtualization, the applications may run in isolation directly on the users desktop system,

or remotely on a server with the application interace displayed on the users desktop, regardless o

the underlying platorm or operating system.

Citrix XenApp is a Windows application delivery system that manages and virtualizes all applications

in the datacenter or optimal application perormance and fexible delivery. With it, you can deliver all

Windows applications to oce, task and mobile users on demand, either run centrally rom the

datacenter or streamed down to the users preerred device.

A single copy o the application is managed centrally, reducing support and maintenance costs byas much as 40 percent. With more than 100 million users and 99 percent o the Fortune global

500 as customers, XenApp is the leader in delivering Windows-based applications with the best

perormance, 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 inrastructure challenges have arisen. This complexity can be attributed

to a number o actors, such as the need to support new applications while continuing support o

existing ones or challenges in scaling the XenApp server inrastructure within a static datacenter.

At the same time, disruptive technological shits, such as the transition rom 32- to 64-bit computing

platorms, have introduced more complexity into XenApp environments. While many XenApp

customers are eager to migrate to 64-bit platorms in order to take advantage o greater memory

limits and higher user densities per server, the problem o supporting old legacy applications remains

a gating actor. Many o these legacy applications are either not supported by or are actually

incompatible with 64-bit platorms. As a result, silos o low-density 32-bit XenApp servers must be

maintained as the rest o the environment transitions to 64-bit, resulting in more complexity combined

with greater management overhead.

Another area o complexity has been the support o multiple geographically distributed XenApp

server deployments. These servers may reside in headquarters or branch oces and be designated

to serve distinct populations o IT consumers. The management complexity and consistency

challenges and entrenched silo mentality have yielded a prolieration o XenApp servers across the


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enterprise. More urgently, as the number o XenApp servers has increased, the costs associated

with powering, cooling, housing and managing all those servers across all those branch ocescontinue to strain IT budgets.

Although XenApp application virtualization has proven itsel eective in accelerating delivery o new

applications, there are still scaling challenges in the datacenter to ensure that the requisite computing

and storage inrastructure supports the new applications. An example o this is an initiative to

minimize the time associated with XenApp server change management, especially as changes need

to prolierate across development, test and production environments. Similarly, IT is looking or better

strategies to provision XenApp servers more rapidly, consistently and economically with ewer resources.

Finally, the uptime and availability o applications remains a primary concern or all IT organizations.

Financial impact to the organization due to both planned and unplanned hardware maintenance can

be easily quantied in XenApp environments. The impact o downtime is especially painul where

the delivery o applications is governed by strict service level agreements or the cost o applicationdowntime can be easily monetized, such as in retail environments. While XenApp technologies like

zone preerence and ailover help ensure the reliability o the application sessions and the routing

o users in the event o site ailures, the uptime provided by an individual XenApp server is still

inexorably linked to the uptime o the underlying hardware. In other words, i a server or component

ails or a server needs to be powered down or hardware maintenance while applications are running,

all user application sessions on that server will be disrupted.

The case or virtualizing Citrix XenApp with Citrix XenServer

While the benets o application virtualization with Citrix XenApp are clear, IT organizations are now

looking to utilize their resources more eectively, 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 benets o server virtualization or their XenApp

environment, there are still concerns about the overhead that virtualization will impart on the application

delivery inrastructure. Early generation virtualization platorms notoriously caused severe drops in

XenApp server scalability sometimes as much as 50-60% degradation in the number o concurrent

users that a single virtualized instance o 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 perormance-optimized or XenApp workloads. Introduced in

XenServer 4.1, the XenApp server template allows XenServer administrators to easily congure

perormance-optimized virtualization or their XenApp server deployments. Optimizing XenServer or

XenApp is surprisingly easy. Administrators simply need to create a new virtual machine usingXenServers built-in App template. Thats it!

How signicant are these perormance optimizations? More specically, what is the quantiable

impact o the server virtualization overhead on a typical XenApp server deployment? Recently, The

Tolly Group, an independent analyst rm, published a scalability benchmark o 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 o just 7.6% or 64-bit XenApp workloads. In other

words, the degradation in the number o concurrent users that a single virtualized instance o 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 o Citrixs leading server virtualization

competitors could support.


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Considering the levels o perormance degradation that are commonly ound in

the real world, achieving virtualization with less than 10% perormance overhead,

is an indication that Citrix has succeeded in tuning XenServer to virtualize

XenApp workloads.

The Tolly Group

Perormance Evaluation o XenApp in a 64-bit Virtualized Server Environment Using

XenServer May 2008

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%.

Virtualization scenarios

There are three main benets that server virtualization with Citrix XenServer can bring to Citrix

XenApp environments.

First, server virtualization can provide signicant benets 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 ootprint in the datacenter

and achieving a ar greater degree o server utilization. Additionally, the isolation and scalability benets

o a 64-bit virtualization platorm can allow multiple 32-bit workloads to be consolidated on higher-

capacity, more cost-eective 64-bit servers.

During internal testing, a three-year old server running Windows Server 2003 32-bit with XenApp 4.5

maxed out at ty concurrent users, while a single 64-bit server easily ran our virtual machines

(running Windows Server 2003 32-bit with XenApp 4.5) with ty users each a total o 200 usersacross our virtual machines. The our virtualized XenApp workloads running on the 64-bit server

delivered the same level o user perormance 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 eciency gains in server platorms in the past ew

years, the hardware investment cost can oten be more than oset in savings on power and cooling.)

Second, server virtualization and dynamic workload management with XenServer introduces a new

and simplied management paradigm or XenApp environments. For example, it is now possible

to manage and provision XenApp servers across both physical and virtual server inrastructure.

This provides a new level o IT fexibility or 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 trac to line-o-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 ar easier to move XenApp servers between the physical

inrastructure, such as what may be deployed in the primary datacenter, and the virtual

inrastructure, such as in the disaster recovery site.


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Third, XenServer adds a new solution to the IT repertoire to enhance the overall availability o

XenApp applications. By virtualizing XenApp servers, it becomes possible to deliver applications toend-users with a ar greater degree o uptime and resiliency. One o the ways that server virtualization

can accomplish this is by eectively decoupling the uptime o the application rom the underlying

hardware using XenMotion, the live migration technology available with XenServer. Furthermore,

eatures such as dynamic workload delivery can simpliy disaster recovery strategies or XenApp

environments, an especially critical capability in the event o total datacenter ailure.

Consolidation

While many physical XenApp servers are already operating at high utilization rates and may not seem

like good candidates or virtualization, there are several common scenarios where IT organizations

can achieve meaningul consolidation o their XenApp servers with XenServer. For example, due to

limitations in the memory architecture in the 32-bit editions o Windows Server 2003, 32-bit XenApp

customers can quickly run into known scalability barriers which articially 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 o memory dedicated or kernel usage and the remaining 2 GB dedicated or application

usage. Although each application gets its own 2 GB o memory, all applications have to share the

same 2 GB o kernel space. As users begin to load a XenApp server, the total number o user sessions

that can be supported by the server ends up being constrained by the shared kernel memory limits.

One opportunity or consolidation is virtualizing silos o 32-bit XenApp servers and consolidating

them on 64-bit servers running XenServer. Consolidation o 32-bit servers on a 64-bit virtualization

platorm allows the XenApp administrator to break through the 4 GB memory barrier imposed by

32-bit platorms, an especially important benet or environments with memory-bound applications.64-bit virtualization also allows XenApp servers to be scaled horizontally. In other words, by moving

to multiple instances o 32-bit XenApp virtual machines on a single 64-bit server platorm, XenApp

customers can eectively increase their XenApp user density per physical server, especially with

new 64-bit x86 servers shipping rom the actory with 32, 64, or even 128 GB o RAM pre-installed.

Finally, or organizations that are not ready to migrate o 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 o 64-bit servers without dictating an expensive

and complex upgrade or the underlying applications.

Figure 2: XenServer can be used to consolidate multiple existing 32-bit XenApp workloads on a single

physical 64-bit server.


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Similarly, many XenApp customers also discover that they can consolidate underutilized XenApp

support and inrastructure servers, such as the licensing server, SmartAuditor server or WebInterace. In many XenApp deployments, there may be the need or a specic, standalone component

and these standalone servers may rarely, i ever, be highly utilized. As a result, lightly-utilized support

and inrastructure servers oten make excellent candidates or virtualization, allowing the XenApp

administrator to achieve consolidation without noticeably impacting end-user experience or

application perormance.

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 signicant.

Finally, by consolidating XenApp server arms, IT organizations can realize a meaningul reduction

in server operating costs. Since much o the cost associated with operating a server is due to

power and cooling consumption, organizations can now green their IT operations and ultimatelycontribute to the consumption o ewer natural resources. These aptly-named green IT initiatives

allow businesses to achieve signicant cost savings through lower utility bills, become a pillar o

environmentally progressive corporate social responsibility programs and, in some jurisdictions,

realize government tax incentives.

Simplied management

XenServer has taken a unique approach to ensure simple, powerul, 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 or a heavyweight operating system. This bare-metal

approach to virtualization diers signicantly rom earlier generation hosted virtualization oerings in

which virtualization sotware ran atop a general-purpose operating system. This had a number o

disadvantages, including severe degradations in perormance and scalability, and the introduction o

additional management overhead or the underlying host operating system. XenServer management

is simple and ecient. 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 fexibility in XenApp environments by allowing application

workloads to be streamed to either physical or virtual inrastructure rom a single virtual disk (or golden

image). This makes it ar easier to maintain, manage, update and patch XenApp servers as well as

ensure consistent process regardless o whether physical or virtual inrastructure is utilized. These

capabilities enable XenApp workloads to be delivered on-demand rather than be physically installed

on top o individual servers. XenServer allows an administrator to create a virtual image o any XenAppworkload and stream it rom 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 rom a single

workload image stored on the network. In some scenarios, up to 1,000 servers, physical or virtual,

can be booted rom the same golden image leading to dramatic reductions in storage usage, especially

or large XenApp server deployments translating into signicant 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 sta increases put tremendous pressure on IT sta to scale out XenApp

application delivery capacity. XenServer can help provision new XenApp servers dynamically, allowing

IT sta to rapidly scale up to meet application demands, and to scale down when demand diminishes.


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Furthermore, with so many complex and multi-tiered XenApp deployments, many customers are

looking or greater fexibility 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 ully replicate each environment, is an arduous task. This is compounded

by the act that test environments are not the main ocus o the business they are temporary and

discarded once they have served their purpose. Rather, the core ocus o 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 all out o 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

inrastructure in their test environments to ensure maximum utilization o limited physical resources, butstandardize on physical inrastructure in production environments or greatest possible perormance

or third-party ISV support. The act that XenServer can provision XenApp workloads agnostically to

physical and virtual inrastructure means that it is not necessary to assign rigid roles to individual servers.

Application availability

Some o the more recent technological innovations in server virtualization such as workload

management, high availability, and live migration have transormed virtualized servers into a more

fexible, resilient and highly available inrastructure compared to their physical predecessors. These

capabilities are nding new uses to help businesses achieve a more agile and responsive IT

inrastructure 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 perormance, 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 aulty or outdated component. During this window, the applications and

user sessions running on that server are interrupted, thus disrupting availability o the application.

The live migration eature o XenServer, called XenMotion, enables IT organizations to decouple

hardware maintenance events rom application uptime by making virtualized application workloads

portable across physical servers. With XenMotion, actively-running virtual machines can be migrated

rom one physical server to another with no application interruption. This allows critical XenApp servers

and applications to remain running even i an entire server needs to be taken down, enabling

Figure 3: Dynamically streaming workloads to physical and virtual machines reduces the storage and

administration requirements or application delivery.


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zero-downtime maintenance. Live migrations o 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 therunning applications.

XenServer also oers built-in high availability or virtual machines as well as third-party options or

ully continuous ault 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

ails. This provides the IT administrator with peace o mind that in the event o a physical host ailure,

application workloads will automatically restart with no requirement or human intervention.

Fault-tolerance extends the concept o high availability by adding an even higher degree o resiliency

and proactive protection against component and system-level ailures. Fault tolerance can protect

applications continuously and ensure zero application downtime or end-user disruption even in the

event o hardware ailures. Fault tolerance or XenServer virtualization is the most cost-eective way to

introduce the highest degree o application resiliency or your most mission-critical XenApp deployments.

Finally, XenServer can help organizations streamline their approach to disaster recovery o XenApp

server deployments by giving IT the ability to rapidly transer their XenApp workloads and applications

rom a primary datacenter to a disaster recovery (DR) site as part o a simple business process. By

leveraging the power o dynamic workload management and virtualization, IT organizations can shit

applications rom one site to another in a ew minutes using a raction o the physical inrastructure

at the DR site.

ConclusionWhile the benets o server virtualization in early generation products were oten oset by perormance

and complexity tradeos, only a Citrix XenServer solution makes virtualization simple and economically

easible or Citrix XenApp environments and other key inrastructure components. The use o XenServer

can result in a consolidated inrastructure that enhances availability and continuity o applications

while helping to optimize hardware capacity utilization without sacricing the perormance o critical

business services. With Citrix XenServer and Citrix XenApp, IT can really do much more with less.

Interested? To download a ree 30-day trial copy o Citrix XenServer Enterprise Edition,

visit www.citrix.com/xenserver/try/.

Figure 4: XenServer can migrate active XenApp workloads to alternate physical machines without

any downtime.


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About Citrix

Citrix Systems, Inc. (Nasdaq:CTXS) is the global leader and the most trusted name in application delivery inrastructure. More

than 200,000 organizations worldwide rely on Citrix to deliver any application to users anywhere with the best perormance,

highest security and lowest cost. Citrix customers include 100% o the Fortune 100 companies and 99% o the Fortune Global

500, as well as hundreds o thousands o 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.

2008 Citrix Systems, Inc. All rights reserved. Citrix, Citrix XenApp, Citrix XenServer are trademarks o Citrix Systems, Inc. and/or one or more o its subsidiaries,and may be registered in the United States Patent and Trademark Oce and in other countries. Microsot and Windows are registered trademarks o MicrosotCorporation in the United States and/or other countries. UNIX is a registered trademark o The Open Group in the United States and other countries. All othertrademarks and registered trademarks are property o their respective owners.

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citrix xenapp and citrix xenserver - better together

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