Desktop Virtualization and Storage
Infrastructure Optimization
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Executive Summary
Getting the most value from desktop virtualization initiative means delivering the same perfor-mance and desktop experience users expect from their traditional desktops. Meeting this goal requires that IT departments make informed decisions about their storage area networks (SANs). In fact, deploying hundreds, or even thousands, of virtual desktop sessions can generate very high input/output operations per second (IOPS) between the storage pool and the server pool. IT departments carefully weigh performance versus storage costs. While, for instance, dynamic tiering technologies provide some relief by offloading the data with the highest performance requirements to high-speed solid-state drives (SSDs), storage costs can rapidly escalate. Accelerating your desktop virtualization initiatives call for best practices to reduce IOPS, optimize shared storage performance, and ultimately reduce storage costs.
In the sections that follow, Citrix® provides an overview of desktop virtualization and unveils
the storage performance challenges of large virtual desktop infrastructure (VDI) deployments. The paper also covers key best practices IT organizations can use to optimize their storage environments to achieve the highest and most cost-effective virtualized desktop performance.
Contents
Executive Summary . . . . 1
Introduction . . . . 2
Common Storage Challenges in Virtualized Environments . . . . 2
Best Practices for Desktop VM Life Cycle Management . . . . 4
Introduction
Enterprises with large VDI initiatives face significant challenges to ensure the optimal desktop user experience. Performance, cost, and complexity are key issues when considering desktop virtualization deployments. Beyond the actual servers and delivery network, the shared storage in many cases becomes the limiting factor for VDI performance. How efficient the storage arrays can process and move data in and out of the physical disk drives is critical.
IT must ensure that their desktop virtualization deployment provide all users with the same, or better, experience than they are used to getting with legacy, non-virtualized systems. Moving large files, interacting with applications and data, streaming multimedia, and projecting collabo-ration with multiple users must “look, feel, and respond” just as users would expect with their local desktops. Anything less than that, and the VDI deployment begins to return reduced value to the enterprise.
Before IT can take steps to optimize performance, it must first understand that different desktop virtualization workloads have their own performance and storage requirements. Throughout this paper, the term “desktop virtualization” refers to a personalized Windows® desktop experience,
typically needed by “task-based,” “knowledge-based,” and “power user” type workers, securely delivered over any network to any device. This option combines the benefits of central manage-ment with full user personalization.
Common Storage Challenges in Virtualized Environments
As with any client-server application, an optimal end-user experience depends on how quickly data can move in and out of the storage arrays. Virtual desktops are no different. However, given that hundreds, or even thousands, of virtual images can be running simultaneously, the input/output (I/O) traffic can be significant. IT departments face several common challenges associated with virtualization and storage pool environments. Desktop virtualization not only has capacity requirements, but also, more importantly, has performance requirements.
Maximizing Storage Capacity
Each virtualized desktop session requires a specific amount of storage space. IT administrators must determine how much storage to assign to each virtual machine (VM) image. They must provision for how much capacity is required to account for every concurrent user, and how much space is required for shared data. Lastly, they must plan for concurrent images all running at the same time. Each of these challenges, if not addressed correctly, will directly impact storage capacity and overall storage costs.
Achieving High Performance
Making matters more challenging, multiple users are sharing the same storage array and disks for their common applications. Different types of application workloads are weighted heavily towards reads or writes or both. For example, a streaming multimedia session may be 90 percent read-based. On the other hand, online transaction processing (OLTP) applications may be 90 percent write-based. Consider the following workload types:
• Task-based workers – Employees in call centers and retail operations perform a set of well-defined tasks. These workers access a small set of applications with specific data access, and they have limited PC customization and mobility requirements. Requirements for I/O generally fall into the six to eight IOPS per virtual disk range.
• Knowledge-based workers – Employees in operations, finance, and administration often require mobility outside their offices. They attend meetings, visit branch offices, and work from home and wireless hotspots. These “anywhere” workers expect access to all of their same applications and data wherever they are. Requirements for I/O generally fall into the nine to fourteen IOPS per virtual disk range.
• Power users – These workers are typically engineers and other technical staff who continually access large pools of data, collaborate remotely on projects, and run large simulation, code development, and other high file and interactive tasks. Requirements for I/O generally fall into the fourteen to twenty-five IOPS per virtual disk range.
Achieving optimal virtualized SAN performance requires a storage infrastructure designed to handle the storage load of a specific environment, applying space and I/O reducing technologies where they make sense. Another challenge is that frequent user file interactions build up redun-dant data. Delta compression can reduce redunredun-dant data written to disk, conserving IOPS. One of the optimization techniques is to use caching close to the VM/HyperVisor. This helps make use of local disk or memory on the hypervisor or a caching appliance in a top-of-rack solution. Approaching the problem using caching can help significantly to reduce I/O traffic to the shared storage.
Managing Storage Costs and Reducing Complexity
Information technology departments must manage their overall costs, and if VDI incurs significantly more expenses, then the virtualization initiative will fail. A key challenge is how to extrapolate the cost of centralized storage from the overall cost of VDI, and how to compare that to the cost of local storage on legacy systems. This becomes even more complex when considering tiered storage solutions that weight performance versus cost. For instance, most storage vendors provide dynamic storage tiering that allocates highly accessed data to faster drives, specifically SSD. The trade-off of latency versus cost is simple. The faster the access and lower the latency, the higher the overall storage costs. While certainly boosting IOPS, these solutions do not address data traffic overhead. They simply move the data faster while not reducing the overall data load. Some vendors and cloud data centers approach the problem by simply charging extra for higher performance, even though much of the data traffic is redundant.
While the above storage challenges may seem daunting, Citrix is addressing each of the above challenges by using innovative solutions and by partnering with other technology experts.
Citrix Desktop Transformation Model
The expert team at Citrix can help customers get from “wow to how” and quickly realize the many benefits of desktop virtualization. This industry-endorsed, repeatable method guides customers in transforming their computing environment from today’s device-centric, distributed management paradigm to a more user-centric, virtualized model. The Citrix Desktop Transformation Model combines the collective experience of thousands of customers and partners across every industry segment that has successfully rolled out millions of virtual desktops and applications to their end-users.
Best Practices for Desktop VM Life Cycle Management
When it comes to VDI and storage optimization, IT administrators have several options. Citrix Provisioning Server™ (PVS) and Machine Creation Services (MCS) each deliver specific benefits.
Most IT departments running virtualization proof of concept projects delay provisioning until later. As time progresses, they start growing their deployment and then run into problems with cost and performance. The result is that they never realize the true benefits of VM storage management. The remedy is to implement the following best practices when moving into or expanding desktop virtualization.
Characterize Application Workloads
As mentioned earlier, each virtual workload requires a different mix of read versus write operations. One best practice is for IT departments to characterize the types of applications and operations that are going to run in the virtualized environment. A key recommendation is to collaborate with a desktop virtualization expert like Citrix that takes a structured approach to workload analysis. This includes first assessing the desktop virtualization task types, designing the optimal solution, and then implementing the plan.
Citrix Provisioning Server
A key question asked by IT departments is how they should provision for virtual desktop lifecycle management. Citrix PVS provides images to physical and virtual desktops by utilizing network booting to obtain the image. Doing this reduces IOPS because only portions of the desktop image stream across the network as needed. Citrix Provisioning Server does require additional server resources, but they can be either physical or virtual servers, depending on the capacity requirements and hardware configuration. Desktop virtual machine writes are typically directed to server local storage, reducing write IOPS for central storage.
Machine Creation Services
Citrix XenDesktop® Machine Creation Services introduced in XenDesktop 5 provides powerful
desk-tops. This function enables administrators to apply updates to the master image once, and then propagate those changes toward all existing virtual machines without the need to re-provision.
Deciding Which to Use: MCS or PVS
The decision between using MCS desktops or PVS desktops depends on the overall architecture. If IT plans to deploy multiple desktop virtualization techniques, like streamed virtual hard disk (VHD) or hosted shared desktops, the PVS infrastructure will already be in place. Thus, expanding to include MCS or PVS will be much easier. However, if the implementation focuses on the use of hosted VDI desktops only, then MCS might be a better option since it requires that the infrastruc-ture deploy fewer servers.
Beyond Citrix PVS and MCS, smart best practices exist that IT departments can implement to optimize shared storage performance. The right choice depends on whether the virtualization deployment is strategic and starting from scratch or the deployment augments existing server virtualization with desktop virtualization.
Reduce Storage Requirements
After deploying VDI, customers may discover that they cannot scale without investing heavily in storage infrastructure. However, IT departments can accelerate their desktop transformation by reducing storage costs and increasing performance, by leveraging innovative technologies available from both Citrix and our partners.
• Storage Optimization:
> Citrix® XenServer® includes IntelliCache to optimize the XenServer hypervisor for use
in XenDesktop hosted-VDI deployments. It caches temporary and non-persistent files for desktop workloads on the local disk of the host server. Citrix IntelliCache merges cheaper centralized storage with local storage for eased complexity and fast desktop performance, while optimizing IOPS, capacity, and cost.
By caching locally, a portion of runtime reads and writes of the virtual machine may occur in lower-cost server attached storage rather than transmitting across more expensive network attached storage (NAS) or (SAN) resources. As a result, IntelliCache can reduce the requirements for central storage by as much as 90 percent. The combi- nation of IntelliCache and MCS allows administrators to deploy and manage all virtual machines as a thin copy of a master VM and build a cache of that image on host servers. > Citrix partner, Atlantis Computing, provides a software virtual machine that runs on
the same hypervisor as the virtual desktops to optimize how the Windows OS interacts with storage. Atlantis storage optimization technology works at the Windows new technology file system (NTFS) protocol layer to offload virtual desktop I/O traffic before it affects storage.
• VDI Storage Capacity Reduction: > Thin provisioning
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> Caching of most frequently used virtual data to reduce overall performance requirements > Inline de-duplication to reduce capacity requirements by eliminating redundant data,
which improves storage utilization and reduces overall I/O activity • VDI Storage Performance Acceleration:
> Transparently caching of I/O operations before they reach the storage fabric > Applying latency improvements to accelerate performance by eliminating disk write
latency or round-trip time > Tiering of storage
Summary and Conclusion
It is the IT department’s responsibility to ensure that the storage infrastructure delivers the highest performing and cost effective desktop virtualization experience. Storage optimization solutions from Citrix and its partners, coupled with best practices, can help reduce data IOPS while decreasing storage costs and maximizing the value of desktop virtualization.
With Citrix XenDesktop and partner solutions from companies such as NetApp, Nexenta, Virsto, and Atlantis Computing, IT gains key technologies to streamline data flow to and from the storage array, while reining in recurring IT costs. By using XenDesktop and best practices for storage optimization, businesses can accelerate their virtual desktop initiatives by the following:
• Accommodate any user scenario and workload with comprehensive virtual desktop and application delivery
• Dramatically improve storage capacity utilization and performance to be on par or better than traditional desktops
• Deliver the highest performing desktop user experience by reducing IOPS, latencies, and redundant data overhead
