Executive Summary
Virtual Desktop Infrastructure (VDI) continues to gain traction in enterprises due to the benefits of centralizing desktop deployments. A successful VDI project will provide a user experience comparable to physical desktops, scale from hundreds to thousands of desktops, and offer a TCO comparable to physical desktops. VDI is very I/O-intensive. The critical challenge is to provide storage with sufficient IOPS performance, scalabil-ity and cost-effectiveness to ensure success. Citrix XenDesktop coupled with Violin Memory’s revolutionary all-silicon Flash Arrays improve boot-up and application access times by 4x, scale to thousands of virtual desktops and deliver the lowest TCO per virtual desktop.
The Business Challenge
Ten to twenty percent of desktops in use today are virtual machines (VMs) running on centralized servers. VDI eliminates the need for traditional PCs and laptops, simplifies desktop administration and updates, and lowers IT capital and management costs. With hundreds or thousands of VMs running on a farm of physical servers, all concurrently accessing shared storage, the storage tier is flooded with heavily randomized I/Os. VDI is an IOPS-hungry application. IOPS demand surges to multiple times the steady state conditions during intensive processes such as boot storms and anti-virus scans.
Main Challenge – Heavy Demand for Storage I/O
If these performance requirements are not adequately met, desktops become slow or unresponsive, especially during performance-intensive processes mentioned above. Users complain, productivity declines, and the success of the VDI project is jeopardized. Workers may even demand their PCs back!
In short, the VDI storage infrastructure must be sized for peak demand instead of aver-age or steady state workloads. It must consistently deliver IOPS comparable to or better than physical desktops in order for a responsive user experience. Moreover, it must be cost-effective on a per-IOPS basis to meet TCO objectives.
The Violin® Memory Flash Solution
Violin Flash Arrays deliver storage at the speed of flash, shattering the old traditional disk I/O bottleneck. Designed for sustained performance and high reliability, capable of expanding to hundreds of terabytes and millions of IOPS, with low (microsecond) and spike-free latency, Violin Flash Arrays are the premier storage solution for VDI.
Next-Generation Flash Architecture
How does Violin Flash Arrays help you achieve the three main objectives of suc-cessful VDI projects?
1. User desktop experience better than or comparable to a physical desktop. Users will judge virtual desktops based on their experience with physical desktops. If virtual desktops are perceived as slow or unresponsive, even intermittently, such as during boot storms, users may not accept them. The speed, throughput, and predictable low latency of Violin arrays are keys to achieving high storage I/O throughput (i.e. 100+ IOPS per desktop), the user receiving fast processing, and overall responsive applications.
2. A Scalable solution, from hundreds to thousands of desktops. VDI rollouts are typically done in phases, starting with a small pilot project followed by adding incre mental groups of users in production. Storage capacity and performance must be able to scale linearly to support all current and future users. Violin Memory’s ability to scale capacity and performance insure that your early investments will grow with you as your VDI project grows.
3. TCO competitive with physical desktops. While hardware costs for physical desktops are generally lower, the centralized administration of virtual desktops reduces management overhead and enables a competitive TCO in the long run, with one important caveat: The server and storage infrastructure must deliver exceptional random IOPS performance in a cost-effective manner. Flash storage excels in high random I/O workloads, unlike traditional disk based storage. Violin Memory Flash Arrays are designed and built for speed and throughput, packing 64TiB of raw flash storage in an economical 3U footprint, with a performance value, at $204 per desktop, is impossible to beat!
Overview: Citrix VDI Capacity Program for Storage Partners
In Q1 2014, Citrix launched a new program designed specifically to address the stor-age needs of customers who are implementing XenDesktop using the VDI FlexCast approach. VDI presents multiple types of data, each with its own unique requirements, to the storage infrastructure tier. Storage in turn can respond to with these requirements using a variety of hardware and software based approaches, some of which can be combined in hybrid solutions. The variety of choices and the differences between them has led to some confusion for customers and partners. To resolve this, Citrix constructed a turnkey “VDI Capacity” test rig in their Santa Clara Solutions Lab. This rig contained the necessary server capacity to generate 750 users of a reference XenDesktop workload. The VDI farm was complete and fully operational with the exception of storage. Citrix storage partners were invited to connect their storage to the VDI farm and participate in a “VDI Capacity” test that simulated of “a day in the life” of a 750 user Citrix farm.
Test methodology
The focus of the VDI Capacity Program for Storage Partners is on provisioning the appropriate amount of storage performance and capacity with a cost-efficient design. Using a simple pass/fail methodology, if a partner’s provided storage solution can suc-cessfully support “a day’s” run to the defined user capacity, while sustaining required performance metrics, the partner passes and the test ends. Once passed, Citrix will describe the storage partner as “750 User Verified” for XenDesktop.
Partner Overview
Business in a Flash. Violin Memory transforms the speed of business with high performance, always available, low cost management of critical business information and applications.Violin’s All Flash optimized solutions accelerate breakthrough CAPEX and OPEX savings for building the next generation data center. Violin’s Flash Fabric Architecture (FFA) speeds data delivery with chip-to-chassis performance optimization that achieves lower consistent latency and cost per transaction for Cloud, Enterprise and Virtualized mission-critical applications. Violin’s All Flash Arrays and Appliances, and enterprise data management software solutions enhance agility and mobility while revolutionizing datacenter economics. Founded in 2005, Violin Memory is headquartered in Santa Clara, California.
For more information about Violin Memory products, visit http://www.violin-memory.com.
Violin Flash Memory Array Portfolio
The Violin Memory 6000 series Flash Arrays deliver up to one million IOPS, latency as low as 100μs and up to 64TB of raw flash capacity in only 3 Rack Units (3U). They include 6 different models with a variety of capacity and performance profiles to fit your particular workload. The 6600 Series uses single-level cell (SLC) flash memory to maximize performance, and the 6200 Series uses multi-level cell (MLC) to optimize density and capacity.
Deduplication Reduces Capacity for Persistent Desktops
Violin Flash Arrays offers inline data deduplication for greater storage efficiency and reduced storage capacity costs – with virtually no impact on performance. Like a hybrid car with better mileage or a house with thicker insulation, deduplication is the feature that makes more efficient use of scarce resources. It scans written data for redundancy and stores only original blocks of data, while redundant data is substituted with a pointer referencing the original data.
For VDI, this means reduced capacity for persistent desktops, which allocate full capac-ity for each virtual desktop. The benefit is desktops can be customized, which users like, but persistent desktops consume more storage capacity and raise the infrastructure costs of VDI. In contrast, stateless desktops use a single “golden” image and create linked clones for each user desktops that only store changed data. With Violin dedupli-cation, enterprises can have their VDI cake and eat it too. In-house testing has found deduplication ratios of 5:1 are typical for VDI environments using persistent desktops. This means users can be given customizable persistent desktops with only one-fifth the capacity normally required, reducing flash capacity and operating costs by 80%.
Violin Benefits for VDI
The exceptional IOPS performance, cost-effectiveness, scalability, power and space-efficiency of Violin Flash Arrays enables you realize your virtual desktop goals: • 5x to 10x improvement in user desktop experience
• 2x to 5x greater desktop consolidation
• Lowest TCO per virtual desktop – Less storage is needed to meet your performance requirement, so less power, cooling and floor space are consumed and operating costs are lower. Ultra-high storage IOPS enables greater server utilization and consolidation, so fewer servers and software licenses are needed.
• Ease of management – Violin Symphony for centralized management. Seamless integration with VMware APIs.
Partner Solution
The Violin Memory solution is simple and elegant, and consists of a single Flash Storage Array from Violin’s V6000 Flash Array line. Since Violin Memory was one of the pioneers of All Flash Arrays and has created 3 generations of products. The VDI solution chosen for this Citrix XenDesktop challenge was one Violin V6264 Flash Array, containing 64TiB of high speed Flash storage, dual redundant flash array controllers, dual SAN gateways, and 8 SAN interfaces (10G Ethernet), all in one 3U package. Every active component in the array is fully redundant and highly available, with no single point of failure, a true Enterprise Class array.
Solution components/ Architecture Design
Configuring iSCSI Using Individual Subnets
Using separate subnets per each 10 Gigabit Ethernet interface will result in the highest performing connection type for iSCSI when connecting to a Violin Array. The recom-mended method to connect the interfaces is to use one subnet for each interface pair. This would have the A1 port on each MG in the same subnet. The total required subnets is 4, and a private network with a netmask of 24 bits (255.255.255.0 or /24) should suit most needs, as shown in the figure below.
An example of using /24 subnets, the subnets are 172.30.11.0, 172.30.12.0,
172.30.13.0, and 172.30.14.0, with the fourth number (octet) being the host identifier. Other size subnets may be used, according to your local network policies, and would have different subnet masks accordingly.
When you are verifying that you have set this up correctly, compare the TX and RX bytes of the “show interfaces” command in the gateways after running for a while. The TX values of eth4, eth5, eth6 and eth7 should be comparable to each other, as should the RX values of eth4, eth5, etc.
One important aspect is to verify your connections making sure that the interfaces sharing the same subnet are connected to each other and you can ping to the adjacent interface. You will use the Windows and Linux MPIO drivers to distribute the traffic across all available interfaces in order to achieve the highest performance for data transfer. The standardized testing environment provided by Citrix only allowed for four 10G ports to be connected from the Violin array to the server, no jumbo frames, and no multipath optimizations.
Test Data Summary
The below table summarizes the performance of the Violin Flash Array during the XenDesktop 750 desktop test. The 750 VMs active row, highlighted in yellow, represents the heaviest load that the test environment generated and is the test data that we will be using in our discussion.
Data Analysis
Notice that both the IOPS and bandwidth Read/Write ratios is a 12.5/87.5 R/W mixed workload. That is very close to a 10/90 R/W mixed workload, so we will use Violin Mem-ory provided test data at that workload to determine the excess performance capacity of the Violin Flash Array, and extrapolate the VDI desktops that could be supported. Below is a table of the performance test data for the very heavy write intensive workload of 10/90 R/W mix.
Conclusion
As can be seen from the analysis above, the Violin Flash Array brings incredible perfor-mance and capacity to the VDI environment, giving you flexible and wide open architec-ture choices for your VDI deployments. Violin 6000 Series Flash Arrays are built from the ground up and hardware optimized to maximize the high-speed, low latency and low energy characteristics of flash memory. The unique architecture of Violin Flash Arrays delivers consistent, spike free, low latency measured in hundreds of microseconds to dramatically accelerate your applications, as well as extreme amounts of IO per second, to drive new levels of storage consolidation. This game changing combination of sus-tained low latency and outstanding performance makes the 6000 Series the storage of choice for scale out virtual infrastructure configurations, such as the Citrix XenDesktop tested here.
Addendum
Minimum storage requirements as determined by Citrix for 750 concurrent VDI desktop users:
• Write Cache Files:
– 6 GB Write cache file per user – 4.5 TB minimum required
– Additional 2.5 TB added to LUN for overhead • User Data:
– 30 GB allowed for each user – 750 * 30 = 22 TB of required space – 3 TB added for overhead
• Total storage capacity required:
– 7 TB for write cache + 25 TB for user data = 32 TB required Citrix Provided Server Configuration
• A single HP C7000 enclosure will be used hold the servers • The enclosure will be in a separate isolated environment • Servers will be BL460c G7 with 2 Procs and 192 GB of memory
– 1 server to contained the necessary infrastructure VMs – 4 servers will contain client VMs necessary to drive work load
• A separate Login VSI 4.0 license will be obtained to further provide isolation • VM Configuration - 32-bit Win7 1.5GB memory, 1 vCPU
– 11 servers will contain XD7 desktops
Citrix Provided Configuration Network Configuration
• FlexFabric will be configured to allow for either Ethernet or Fibre connectivity from the blades. These will be connected to a 4gb Brocade switch
• Four networks will be created:
– Network 1 – internal to HP Virtual Connect for PXE boot of VMs, 5 gb – Network 2 – Connection to lab storage and management, 1gb
– Network 3 – Production network for connection between clients and XD VMs, 5 gb
– Network 4 will be either:
• Connection to vendor storage for using iSCSI, 9 gb OR • Fibre connection to SAN for vendor storage
XenDesktop Configuration • XenDesktop 7 will be used
• Provisioning will be done with PVS version 7.0.0.46. Due to MCS working best with file based storage and not all vendors supporting file based storage (NFS), PVS will be used to provision the desktop VMs. This will create a write-intensive environment. • One each broker (DDC) and PVS VM will be created to support the Infrastructure Storage Configuration completed by Violin Memory
• Storage Array: Violin 6264
• No of iSCSI Targets: 4x 10GBE used for test ( max-8 ) • MTU: 1500 used for test (max -9000)
• Total Raw Storage: 64 TiB
• Total Usable Storage: 40 TiB ( after RAID) • Used Storage: 37TiB ( carved into thick LUNS)
• Utilized storage by VM’s: 7TiB ( cache file similar to vmswap – Golden image is not on Violin.
• LUN count and size: 11 x 1 TiB LUNS + 1 x 27 TiB LUN ( thick) • LUN block size: 4096 bytes
• NTFSFilesystem block size: 4096
Definitions VM definitions • Infrastructure VMs:
– All will be 64-Bit Windows 2012 – AD VM – 4GB memory, 1 vCPU
– DDC VM – 8 GB memory, 2 vCPU – locally configured SQL – PVS VM – 4 GB memory, 2 vCPU – locally configured SQL • Client VMs
– 32-bit Win7, 1.5 GB memory, 1 vCPU • XD VMs
– 64-bit Win8, 1.5 GB memory, 1 vCPU Login VSI
• Login VSI 3.7 will be used
– VSIShare will be inside the chassis – IOPs medium work load will be used
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