A while ago we hosted the TechTalk “Virtual Desktops – A design for small environments”, which had more than 1.100 live attendees. During that session we ran a live Q&A with the intention to answer all questions that the attendees might have. The flaw of the plan was that we underestimated the amount of questions and although we extended to Q&A part to 60 minutes and had three panelists (Dan Faller, Tarkan Kocoglu and me) on the phone we could not answer all of them. To cut a long story short, below you can find the first third of the open questions:

Q: should I run Controllers and data storage servers on same hypervisors if I already have server virtualisation infrastructure?
A: Hosting virtual desktops, XenDesktop Controllers or other infrastructural systems on the same virtualization platform is fine, although you should avoid single points of failure (SPoF) that can affect all virtual systems at all cost. Typical SPoFs are single instances of SCVMM or vCenter, or hosting all infrastructure systems on the same host.

Q: What order of benefit would intelicache on xenserver5.6 give locally stored MCS images?
A: The IntelliCache feature was introduced with XenServer 5.6 FP1, which is currently not supported with XenDesktop 5 as indicated here: http://support.citrix.com/proddocs/topic/xendesktop-rho/cds-sys-reqs-host-rho.html.

Q: I have approx 300 users spread accross 27 sites some of which have only small wan links <2mb can we still consider Virtualisation?
A: I assume virtualization means centralization in this context. The answer is it depends. It depends on the applications your users will run inside the virtual desktops and the user pattern. Given that your users are equally spread across all 27 sites this means you have 11 users per site on average. In our User Bandwidth Requirements Guide (http://support.citrix.com/servlet/KbServlet/download/24560-102-647702/XD%20-%20Planning%20Guide%20-%20User%20Bandwidth%20Requirements.pdf) we describe that an office task user with our particular workload will consume 43kbit/s. Multiplying this bandwidth requirement with 11 users, we see that approx. 473kbit/s will be required, which fits your 2mbit/s constraint (assuming there is not more than 1.5mbit/s competing traffic on the same WAN links).

Q: what sort of bandwidth do you require for users over a WAN?
A: The bandwidth required per user depends on the applications running inside the virtual desktop and the user pattern. Please check http://support.citrix.com/servlet/KbServlet/download/24560-102-647702/XD%20-%20Planning%20Guide%20-%20User%20Bandwidth%20Requirements.pdf for some information on this topic.

Q: does every clone machine has unique SSID?
A: Every machine based on MCS or PVS will have a unique computer account within Active Directory (Domain SID), but keep the same local SID as the master. Assuming you’re not relying on machine local user accounts, this does not impact security as outlined by Microsoft’s Mark Russinovich (http://blogs.technet.com/b/markrussinovich/archive/2009/11/03/3291024.aspx).

Q: In read-only mode does the virtual desktop have to be re-added to Active Directory every time it is ‘refreshed’
A: No. Machine Creation Services as well as Provisioning Services will always assign the same Active Directory Computer Account to a virtual machine, as long as the virtual machine does not get deleted from the hypervisor (MCS) or from the Database (PVS).

Q: What is the Best Option for using User Profiles in Xendesktop 5
A: This is depending on your requirements. Please check http://support.citrix.com/servlet/KbServlet/download/26480-102-650196/XD%20-%20Planning%20Guide%20-%20User%20Profiles.pdf for further information.

Q: After updating the master image, how does this affect the user experience/customisation in their DIFF image ?
A: Updating the MCS master image does not impact the dependent virtual desktops, as these actually link to a dedicated snapshot of the master rather than the actual virtual disk. For persistent desktops, that keep user changes even over reboots a central update of the master snapshot is not possible, as indicated here: http://support.citrix.com/proddocs/topic/xendesktop-rho/cds-update-master-vm-rho.html

Q: To deploy VDs on WAN do we need any H/W from Citrix
A: No, you don’t necessarily need any additional hardware like Citrix Branch Repeater, but this can lower the bandwidth requirements and enhance the user experience tremendously, as indicated here: http://support.citrix.com/servlet/KbServlet/download/24560-102-647702/XD%20-%20Planning%20Guide%20-%20User%20Bandwidth%20Requirements.pdf

Q: How does XenDesktop deal with offline branch situations. Eg if the branch network goes offline
A: If a branch is offline the user cannot access the virtual desktops anymore and existing user sessions get disconnected. Therefore it is important to have a redundant network connection for every branch, data center and even component. Just as a side note: The same “risk” exists for every centralized infrastructure. Even if just the backend systems are centralized users cannot work if the network is down.

Q: which is best to use for remote access Citrix Secure Gateway or Access Gateway ?
A: This depends on your requirements (security / functionality / performance). In general using Access Gateway is best as it offers a much higher performance and much more features at a higher level of performance than Secure Gateway, which functionality will not be enhanced anymore.

Q: pLEASE WHAT ABOUT FAULT TOLERANCE? ANY COMMENTS ON THIS ARCHITECTURE
A: Please check this document: http://support.citrix.com/servlet/KbServlet/download/21772-102-641467/XD%20-%20HA%20-%20Reference%20Architecture.pdf

Q: Hi, how do you implement hight availability with MCS ?
A: Machine Creation Services depend on XenDesktop site services, that are automatically load balanced / high available within a XenDesktop site of two or more XenDesktop Controllers. Additionally it is important to attach the storage infrastructure redundantly to the hypervisor hosts, as all desktops / master machines need to access it during runtime.

Q: We have a branch office with 7 employees, but we have high latency, over 70 ms. Will we have a good user experience with Citrix Xendesktop?
A: This depends on the requirements of the users, but for typically office workers a latency of 70ms will not impact the user experience.

Q: what is the recommended storage type for Xendesktop 5 NFS or iSCSCi?
A: The recommended storage protocol for MCS based infrastructures is NFS, as it offers Thin Provisioning capabilities. For Provisioning Server based infrastructures block based storage protocols such as FC or iSCSI is recommended as indicated here: http://support.citrix.com/servlet/KbServlet/download/24250-102-647569/Advanced%20Memory%20and%20Storage%20Considerations%20for%20Provisioning%20Services%20v3_0202.pdf

Thomas