Protect your Journey to a Successful Virtual Desktop Infrastructure

POSTED BY : Specialist - Cloud Services
Thursday, April 18, 2013

Virtual Desktop Infrastructure - A quick Introduction:

Desktop Virtualization is a software technology that separates the end user desktop environment and associated application software from the end-user device.

Virtual Desktop Infrastructure (VDI) in a nutshell is to provide users with access to server-hosted desktop operating systems on nearly any client device, nearly anywhere in the world.

VDI has a lot of advantages over traditional desktop environment including:
- Easy Management
- Easy Windows 7 Roll-out
- Increased Desktop Life
- Elasticity
- BYOD

With windows 7 roll-out being a key business initiative, it has been observed that more than 80 percent of companies are currently using or considering Virtual Desktops for an easy roll-out.

Interest is finally translating into implementation, over the past years we have seen a huge increase in VDI deployments. We have also seen many challenges faced by these organizations while attempting to implement a reliable and scalable VDI.

Dynamic scalability, unsupported protocols, poor end-user performance are the major obstruction in the success of VDI rollouts, especially in larger organizations.

Major challenges being faced are because of incomplete assessment of end user workspace and performance bottleneck with compute, storage or network. Below exercise will help you in defining end user workspace and validating the hardware architecture for enhanced performance, before implementing VDI.

How concrete is your Initial Study?

Many organizations have chosen a quick way of sizing i.e. multiplying the average RAM size of end user physical desktop to the number of users in correlation with the CPU requirement (heavy, medium or light) which is used for determining the number of blades server required to host the infrastructure.

This sizing assumption is great for the initial steps where an organization is still trying to see the feasibility of VDI for their end users however designing a solution based on this assumption and completely ignoring the other two most important components of VDI i.e. Storage and Network may result into an underperforming or over utilized end user Virtual Desktop Infrastructure. Unfortunately the same cannot be validated without the actual load and hence cannot be validated in Pilot either.

Moreover, understanding the end user workspace including the applications being used is again an important exercise to see the feasibility of Virtual Desktop Infrastructure for end users.

Hence, it is highly recommended to do a complete study of end user workspace requirement before virtualizing the same.

Capturing key matrix for initial study is the most important step for defining and designing a comprehensive, well-utilized and well managed Virtual Desktop Infrastructure. Below is a quick synopsis of how should an organization capture various data point and align them together to achieve the desired result.

Complete Application Inventory Data on all hardware, including desktops and laptops should be collected as the first step of VDI Assessment. Application inventory should capture detailed information about each application, including:
- Application resource requirements (total and average CPU, memory, IO)
- Total number of application users
- Average launch delay
- Application usage
- Application Data
- Licensing Type
- Application Readiness for Windows 7 / Windows 8 (32-bit and 64-Bit)
- Application Readiness for Terminal Server including Windows Server 2008 R2 and 2012

Please note if there is a dependency on applications which are not yet ready for Windows 7 its recommended to include various application Virtualization solution like Xen-App -05 or running the application in Windows XP Mode on Microsoft virtual PC in the initial design itself.

Once you have the application inventory the next step is to capture the User Workspace Resource requirement including:
- CPU Utilization (Peak and Average)
- Memory Utilization (Peak and Average)
- Network Utilization (Peak and Average)
- Storage Utilization (Peak and Average)

Next step is to capture User Profile requirements including:
- Profile Type (Local, Roaming, Mandatory or Hybrid)
- Average Profile Size
- Application Data
- User Data

Last but not least is the complete understanding of Group Policy to understand the workspace thoroughly.

Above data should help you in categorizing users into different groups based on resource requirement, application type and profiles being used. The categorization should broadly divide the users in three groups based on the resource requirement as mentioned below:
- Light Weight
- Medium Weight
- Heavy Weight

Based on the application inventory you should be able to finalize the number of use cases and the golden images associated to it.

End-Result of this exercise should be profiling the users as Heavy, Medium or Light weight users and the golden Image to be used for each department.

This data is generally provided to various technology experts for designing the overall VDI Architecture which is scalable, highly available and performance sustainable VDI Design.

Here are few quick tricks to validate the overall hardware architecture for performance.

Validating RAM & CPU Requirement

The amount of memory assigned to each virtual desktop varies according to the memory requirements of the workload(s) that they support. Most of the time, memory requirement is calculated by multiplying the number of light users by 512MB, normal users by 1024MB and heavy users by 2048MB; this should be a direct input from Profiling template created in initial study and it should also include operating system overhead.

The user density of each vCPU Virtual Desktop will vary according to the workloads that they support and the processor architecture of the virtualization host.

The following table shows typical memory specifications for each processor specification:

Sockets

Cores per Socket

Total Physical Cores

Total Virtual Cores

Host Memory (GB)

2

6

12

24

96

2

8

16

32

128

2

10

20

40

128

4

6

24

48

128

4

8

32

64

192

4

10

40

80

256

 

Validating Storage IOPS Requirement

The trick is to calculate the right ball park using standard and accepted approach.

First step is to collect the front end IO requirement. Each light user requires an average of 2 steady state IOPS, each normal user requires an average of 4 steady state IOPS and each heavy user requires an average of 8 steady state IOPS. Please note this should be a direct input from Profiling template created in initial study. The ratio is about 80/20 Writes/Reads for each user.

Let us assume that we are sizing for 1000 Normal Users. With 80/20 of 4 IOPS a desktop is 3.2/.8 writes/reads for each user. For 1000 users we need 3200 Write IOPs and 800 write IOPs.

Step two is choosing the RAID Level. Generally we choose for maximum capacity hence for this calculation I have chosen RAID 5. With the Parity of 4 we would need 12800 write IOPs and as read does not carry penalty we would need 800 read IOPs and hence a backend IOPS pool size of 13600 IOPS.

RAID

Write Penalty

0

1

1

2

5

4

6

6

DP

2

10

2

 

Last step is to calculate how many disk spindles it would take to meet this requirement. Assuming 180 IOPS per spindle which is a typical 15K RPM drive at about 80% full for, 13600 IOPs would need 75 (EA) 15k RPM spindles to meet the backend IOPS requirement.

Disk Speed

IOPS

15,000

175

10,000

125

7200

75

5400

50

 

Choosing RAID 10 will affect the overall storage capacity requirement, but with 2 write penalty it can reduce the overall IOPS requirement to 50%.

As a recommendation, it is a best practice to refer storage vendors with VDI Reference Architecture to validate your numbers and getting their recommendation on reducing the disk requirements further by means of implementing their latest storage features.

Validating Network Bandwidth Requirement

Regardless of the flavour of virtual desktop being implemented (hosted shared, hosted VM-based VDI, local streamed, etc.), the network plays a critical role, especially for remote and branch office users. If the network bandwidth is not planned properly, users will most likely experience poor performance with their virtual desktop.

By calculating the percentage of time a user is expected to be doing certain activities, a rough estimate can be determined for network bandwidth requirements, which is shown in the follow table:

Parameter (medium workloads)

Average Network Consumption kbps

Usage Minutes

% of Time

Bandwidth Requirement

Office-based

43

240

44.44%

19.11111111

Internet

85

60

11.11%

9.444444444

Printing

555

15

2.78%

15.41666667

Flash Video

174

30

5.56%

9.666666667

Standard WMV Video

464

10

1.85%

8.592592593

HD WMV Video

1812

5

0.93%

16.77777778

Idle based on active applications

0

180

33.33%

0

Burst

1812

Average

79.00925926

Validation of the same using initial assessment reports will ensure the complete understanding of the network requirement.

Caution must be taken when using the average value. By averaging out the bandwidth requirements across an entire day and across many users, there may be lack of bandwidth if a large percentage of users have a large burst in traffic at the same time. Based on the expected user habits, it is advisable to include a bandwidth burst calculation for unexpected bursts of traffic.

And that's the final step in this sample exercise. I hope this helped to explain how to quickly define the end user workspace and validate the hardware architecture of VDI.

Disclaimer: The view expressed herein are those of the author and Microland expressly disclaims any liability arising from its publication on our website.

 

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Sunny Malik
Specialist - Cloud Services
Desktop Virtualization