I finally have a moment to sit down and respond to the unanswered questions from my Hyper-V Planning for XenDesktop webinar on June 15, 2010. Below is a list of questions that came in during the webinar that I did not have time to answer directly. Some of the questions have been altered slightly to clarify and adjust for typing errors. Questions answered during the broadcast are not included below.

Q: 2 Gig space for profile?
A: Since this question is not very specific, I will take a moment to provide my interpretation of it. If I have incorrectly interpreted it, please provide feedback via the comments section below. I believe the question is asking why we would recommend a 2 GB write-cache file for just a user profile.

The answer is because the write-cache file contains more information than just the user’s profile. First, if the virtual machine is not rebooted between each user (such as discussed in my earlier blog entitled, Selecting a XenDesktop Logoff Behavior you might have more than one user profile. Second, the write-cache drive contains the system page file, which normally is at least the size of the RAM installed on the virtual machine, which is a minimum of 1GB. Finally, other files, such as temp files, log files, etc. need a space to write their information.

Could the write-cache drive have been smaller? Certainly, but given the size of the page file (1 GB in this environment) I would not suggest a write-cache drive that was smaller than 500MB plus the page file size or 1.5GB in this environment.

Q: Does XenDesktop support Ubuntu or any other Linux distribution?
A: Depends on whether you mean supporting it from a client or server-side. We have Citrix Receivers (ICA Clients) for Linux therefore, from the client-side Linux is fully supported. If you mean from a server-side, where you are remoting into a Linux machine using ICA this is currently not possible. XenDesktop Virtual Desktop Agent (VDA) is currently only distributed as a Windows service, so it only runs on Windows operating systems.

Q: For a 2000-desktop Windows 7 deployment, what would you suggest as a best practice in terms of storage IOPS, vCPUs, and RAM.
A: This is one of those questions where I could literally spend hours discussing the requirements. However, I will try to sum them up in a few short statements. First, Windows 7 runs lovely on 1 GB of RAM and 1 vCPU. If you have applications that need more horsepower, than the best course of action would be to pilot the application with different resource configurations to determine the optimum configuration to meet the user’s expectations. The more difficult question to answer is the storage IOPS requirement. Assuming you had a 30-second Windows 7 login time frame and you wanted all 2000 users to login within a 30-minute time period, I would suggest storage that supported a peak capacity of close to 16,000 write IOPS. Scalability guidelines can be found on the Citrix eDocs website and navigating to XenDesktop >> XenDesktop4>>XenDesktop Scalability Guidelines.

Q: Have you run over iSCSI or only Fiber Channel?
A: Finally, an easy short answer. Yes, I have run over both storage protocols. The 3500-desktop farm scalability test was performed on an HP P4500 iSCSI SAN.

Q: I would like to build a server for a small site (10 users and maybe 5 demo users) can we go all virtual on the servers?
A: Absolutely. For that small of a load, the virtual servers should have plenty of horsepower available.

Q: Is Provisioning Server cluster aware for high availability?
A: Engineering has not tested with a SQL cluster. However, based on past research, it should work because in a clustered configuration there is only one connection string. Therefore, when an error is detected and a reconnection is attempted using the same string, it should reconnect successfully. Because the PVS stream service reconnects when an error is detected, a restart is not necessary.

Q: Does Microsoft have any plans to make migration automatic like VMWare anytime in the future?
A: I have heard that this is something they are working towards. However, I am not a Microsoft Product Manager, and cannot speak for Microsoft. I am sure they realize it is a deficiency.

Q: What are the advantages of Hyper-V in contrast to other virtualization solutions, for example VMWare ESX?
A: Good question. I tend to look at hypervisors as a commodity, where you can just pick the one that best meets your needs. In the case of Hyper-V, I personally believe that Windows 7 performs better on Hyper-V with XenDesktop than with VMWare ESX or even XenServer. I think that cost is also another factor that should be considered when looking at the advantages of Hyper-V. In the end though, it comes down to your preference for a feature set, the commercial aspect of it, and sometimes what you already have in your datacenter.

Q: What is a good or ideal size host in terms of CPU and memory?
A: Well, I personally prefer the Nehalem L55xx series for processors; however as everyone warns your mileage may vary, so look at the performance reports for similar workloads and choose the most appropriate processor model. For memory, look for the most efficient cost point where the RAM is still sold in affordable chip sizes. For instance, on a blade server with 12 memory slots, the 8 GB chips have a good price point so you can go 2 quad-core Nehalems with 96 GB of RAM and you end up with a VM density of around 10 VMs per core.

Q: What is the response time recommended to have a good performance?
A: I believe the question is referring to the acceptable response times for end users. When we do large-scale testing of XenDesktop we figure response times inside the VM should be under two seconds. This is a bit of an arbitrary number, but it is usually sufficient to estimate at what point a session is failing. Obviously, sub one-second response times would be the best.

Q: What would be a best practice for user’s profile control and management?
A: This is one of those questions where the response could be a whitepaper. I will forgo the lengthy analysis and provide a few general guidelines. First, if you are using Provisioning Services and standard-mode disk images, you will need to store the user’s profile data off of the write-cache, so roaming profiles are required. You can leverage the User Profile Manager that comes with XenDesktop or spring for a more third-party solution such as AppSense. Generally if you plan on supporting both v1 and v2 user profiles in the environment, AppSense is a great way to go. Second, use folder redirection where possible to redirect common local storage locations to network folders so the data is available on all the workstations. Finally, using login scripts or home drive mappings to create consistent data views will allow users to have the same look and feel no matter which desktop they receive.

That concludes the unanswered questions from my webinar. I hope you find the answers helpful. If I misunderstood your question, feel free to clarify it as a comment below.

I feel bad that I did not have an opportunity to answer all these questions during the webinar, so I am actually considering a new webinar format which I tentatively refer to as “Meet the Architect Q&A.” Essentially the concept is an open forum, with no prepared material where the attendees provide live questions and I spend the entire time just answering the questions. This format will basically give you, my readers, and opportunity to interact with me and get my opinions or advice on questions or challenges you are facing.

Let me know what you think about the Meet the Architect Q&A by commenting on this blog. I really don’t want to end up with a 60-minute webinar and no participants.

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