Daniele Tosatto

If you were asked what desktop resources your needed how would you answer? If you ask me what type of desktop I need, I’m going to say, 2+ cores with at least 4+ GB of RAM, 500+GB hard drive, etc. If you look at what I really need, you will see 1 core and maybe 2-3 GB of RAM. In fact, when I look at my resource consumption, I get close to 2.5 GB of RAM by the end of the day due to the number of applications I have running, memory leaks in some of my applications, and applications not freeing up memory when closed.

Like me, many users only consume a fraction of their total potential desktop computing power, which makes desktop virtualization extremely attractive. By sharing the resources between all users, the overall amount of required resources is reduced. However, there is a fine line between maximizing the number of users a single server can support and providing the user with a good virtual desktop computing experience.
Improperly allocating resources to the virtual desktops is the 7th most common mistake make. Other mistakes, discussed previously, include:

10. Not calculating user bandwidth requirements

9.   Not considering the user profile

8.   Lack of Application Virtualization Strategy

One of the lessons we learned from virtual desktop implementations is trying to push the hypervisor, any hypervisor, too hard results in a poor user experience. The following recommendations help optimizing the environment by focusing on the hypervisor:

Parameter	Hypervisor	Description
CPU Allocation	Citrix XenServer Microsoft Hyper-V VMware vSphere	Users should start with a single vCPU and be granted a second if needed due to the following: Most user-based applications are only single-threaded and will not benefit from a multiple CPU configuration. Many user applications do not require significant amounts of processing, which negates the need for more CPU power. By allocating multiple vCPUs for each virtual desktop, extra resources are required to switch requests across the different cores.
Command Tuning	Citrix XenServer Microsoft Hyper-V VMware vSphere	The XenDesktop controller sends low-level commands to the hypervisor layer to perform tasks on the virtual machines (start, stop, reboot, etc). If too many tasks are sent out simultaneously, the connection to the hypervisor layer can become sporadic. These tasks often have a large impact on the server resources, which impacts the users. It is advisable to throttle the number of commands sent
Transparent Page Sharing	VMware vSphere	Transparent Page Sharing allows the vSphere hypervisor to share portions of memory that are identical between virtual machines. This has the potential to improve the virtual desktop performance by having a positive impact on memory consumption.This feature will typically only provide value in older operating systems, like Windows XP and Windows Server 2003, which have 4KB memory pages.  Newer operation systems, like Windows 7 and Windows Server 2008, have large memory pages (2MB) by default. The larger memory pages makes the likelihood of finding exact duplicates of memory very difficult.
Memory Ballooning Memory Overcommit	VMware vSphere Note: XenServer and Hyper-V support for dynamic memory is new. It is assumed the results will be similar, but testing is required.	Memory ballooning or memory overcommit shifts RAM dynamically from idle virtual machines to active workloads. Memory ballooning artificially induces memory pressure within idle virtual machines, forcing them give back memory so other virtual machines can consume it (each hypervisor does it differently but the overall concepts are similar). In practical applications, this has shown to be an impediment to positive user experiences. Forcing virtual desktops to free up memory is only a temporary solution. If a large group of idle or low-usage virtual desktops become active (after lunch, for example), they will require more memory. But if many of the virtual desktops on the same hypervisor are experiencing increased loads, where will the extra memory come from? With no free memory, the hypervisor is forced to page to disk, which is slow. A desktop is not a server. A desktop is running desktop applications which often have more memory leaks and poor cleanup processes when compared to server applications. Most desktops consume more memory as the day progresses due to these leaks, which will put strain on any overcommit feature. It is advisable to disable this feature.

XenServer 5.6 was announced a couple of weeks ago at Citrix Synergy, and this morning (Eastern US time) Citrix posted it for download on citrix.com.  If you are considering XenServer for the first time, or looking at upgrading to 5.6 from a prior version, here’s some information on what’s new that will help you:

Dynamic Memory Control.  Let’s say you have a few XenServer hosts.  You need to spin up some more VMs, but your VMs are configured to use all available resource pool memory.  However, you know that some of the existing VMs aren’t using all the physical memory you’ve allocated.  With XenServer 5.6, you can set memory ranges for VMs so that you can squeeze the physical memory used for existing VMs in order to let new ones on.  If you find that one or more VMs operating near the lower limit requires more memory, you can increase the minimum level on the fly without rebooting.

Role-Based Administration and Audit.  You’re the primary XenServer administrator.  You have a junior admin that you want to provide a lower level of access within XenCenter so that they can start/stop/reboot/snapshot VMs without either 1. bothering you to do it for them all the time, or 2. Giving them full access to the XenCenter console where they have access to networking and storage configurations.  If that junior admin deletes a VM, you’ll have an audit trail with a record of this change, and when it was performed.

Heterogeneous Pools. Let’s say you have a pool of 5 XenServer hosts, which run on year-old hardware with Intel Xeon 5400 processors.  Now you buy a couple of new servers, which have new Intel Xeon 5500 processors. With XenServer you can join them to the same pool and enable XenMotion, HA, Shared Storage, and Workload Balancing. In the past, you could “force join” the newer servers to the existing pool, but you’d have to be careful not to XenMotion between different processor types.  This feature works with Intel processors with “Flex Migrate” capability and AMD processors with “Extended Migration” features.  Note that live migration between Intel and AMD does not work. Citrix’ve added a new section on the HCL with the tested configurations.  Those that aren’t listed can be added by running through the Citrix Ready XenServer hardware test kit.

Memory Snapshots and one-click revert.  In addition to disk snapshots for backup, now you can snapshot the live running state of a VM.  In previous versions of XenServer, reverting to your snapshot was a multi-step process that was not ideal.  Now you just click “revert” in the snapshot manager.

Dynamic Workload Balancing with Power Management.  If you have a XenApp farm running 24×7,there is quite a bit of power wasted by those servers during nights and  weekends when only a handful of users are accessing applications.  Workload balancing can be scheduled to consolidate all of your idle XenApp servers on as few hosts as possible while powering off the newly vacated XenServer hosts. In the morning or after a weekend, those machines will power on and the VMs will be redistributed to handle the load.  Additionally, Workload Balancing includes a fully-automated mode with some new configuration options.  Example: if you have some VMs that you don’t want moving around, simply start those VMs on a specific host and exclude that host from WLB computations.

Increased scalability.  We’ve doubled support limits for logical processors and memory to 64 and 256 GB, respectively.  Up to 16 NICs per host are supported as well.

Updated Support for Provisioning Services (PVS).   PVS 5.6 has been updated, and includes a helpful new vDisk imaging wizard.   XenCenter is now more aware of PVS boot scenarios, namely through “boot from network” options in the new VM setup wizard.  One thing we’d like people to try (call it a “Tech Preview”) is streaming of XenServer bits themselves, in addition to VMs.  The eventual goal here is to greatly simplify management of XenServer updates and upgrades, just as PVS has done for XenApp and XenDesktop VMs.

Enhanced XenCenter. Did you run the XenDesktop setup wizard incorrectly and create a bunch of VMs that you now need to delete?  Use the multi-select feature, right-click, and select “delete.”  Need to start or shutdown a bunch of VMs at the same time?  Another good use for the multi-select option.  Other useful additions include one-step “VM move” (powered down) from array to array. Try right mouse clicking on a custom template and select “Instant VM from template.” You won’t be prompted to accept all the defaults, which you probably click right through anyway.

Enhanced support for iSCSI arrays with multi-IQN / IP configuration.  DataCore SANMelody is an example of an iSCSI array that advertises multiple IQNs with multiple IP addresses.  With 5.6, we aim to make the setup of XenServer with SANMelody arrays much easier with the wildcard IQN scan option.

OEM edition simplification.  We used to assist with the creation of HP and Dell-specific versions of XenServer, which they shipped onboard their servers.  This had some issues.  One key example: though “Update” releases were made available for OEM editions, individual hotfixes were not.  No more.  Now we have one set of bits and HP and Dell apply hardware specific “supplementary packs” which contain their management agents and other hardware-specific components.  You can also support BIOS locking if you have an OEM version of Windows that you want to run as a virtual machine on your XenServer host.

Advanced Edition.  HA, Dynamic Memory Control, Alerting, and Performance History for $1,000 per server. Note: for a full list of the features in each edition (including Free) see here:

Server-based pricing. This isn’t “new” per se, however it’s starting to matter a lot more when you compare costs of XenServer and vSphere on some of the latest servers.  Dell R815 and HP DL385 G7 servers now ship with 12-core Opteron 6000 processors.   The problem for VMware customers is that they won’t allow you to run vSphere Standard or Enterprise Edition on those servers.  In other words, VMware hates Moore’s Law.  With XenServer, we don’t care how many cores or sockets the server has; you pay the same price with any configuration.  Citrix loves Moore’s Law.

Initial SR-IOV platform support for NetScaler VPX. If you’ve got a server with an Intel SR-IOV capable NIC, you will soon be able to achieve near line-speed network performance to a XenServer virtual machine.  Initial tests within Citrix have shown ~ 108 Gbps of aggregate bandwidth to a NetScaler VPX virtual machine.  Note that the real benefit of this will arrive when we have a version of the NetScaler VPX that can use this platform capability (later this year).

StorageLink Site Recovery.  You’ve got a secondary site where you want to replicate all your virtual machines in case disaster strikes your primary site.  StorageLink Site Recovery simplifies the process of setting up this replication and recovering virtual machines in the DR site. Check the StorageLink HCL for arrays that initially support Site Recovery.

Citrix License Server integration.  Paid versions of XenServer now require a Citrix License Server.  Here’s what you need to know:

1. The Free version of XenServer continues to use the file-based activation process, so a license server isn’t required if you are using Free XenServer.

2. Unlike with prior versions of XenServer, licensing is enforced.  Before you upgrade any existing 5.x systems to 5.6, verify that you have the right number of licenses allocated to you via your mycitrix.com account. Note that there is a 30 day grace period after an upgrade, which gives you plenty of time to get your License Server set up.

3. In addition to the existing Windows-based License Server, we’re making a License Server virtual appliance available as well.  Just import it, run through a short configuration, and use a browser to upload your license files.

For more information on 5.6 licensing, see CTX125301.

Was anything removed from the product in 5.6?

Not much.  The legacy Linux P2V tool in the installer is gone, though it wasn’t of much use any more since it only worked for very old distros. We’ve also dropped Debian Etch (4.0) support since it no longer receives security updates.  Those of you who look closely might find that the new “Demo Linux VM” template is, shall we say, eerily similar to Debian Etch.  It’s not recommended for production use, and we have this solely because so many of you told us you liked the built-in Linux distro for testing and demonstration purposes.

Citrix Support is focused on ensuring Customer and Partner satisfaction with his products. Citrix is working on multiple items to help make it easier to find answers and solve problems via self-service avenues, all of which are available to all his Partners and Customers to leverage.

Last November Citrix launched the How To video initiative and to date have over 100 videos covering 12 products available on Citrix TV.

The following is a list of the TOP 5 videos since launching the initiative.

#1 How To: Create a VM Template and Deploy using XenDesktop Wizard

#2 How To: Configure USB Support on XenDesktop

#3 How To: Convert a Physical Machine to a Virtual Machine

#4 How To: Deploy Citrix Clients via Web Interface 5.2

#5 How To: Configure Pass-Through Authentication with Web Interface 5.2

Current video series available on Citrix TV are:

• Citrix XenServer – http://www.citrix.com/tv/#series/137
• Citrix XenApp – http://www.citrix.com/tv/#series/131
• Citrix XenDesktop – http://www.citrix.com/tv/#series/135
• Citrix NetScaler – http://www.citrix.com/tv/#series/133
• Citrix Provisioning Services – http://www.citrix.com/tv/#series/136
• Citrix Web Interface – http://www.citrix.com/tv/#series/129
• Citrix Merchandising Server – http://www.citrix.com/tv/#series/124
• Citrix Password Manager – http://www.citrix.com/tv/#series/126
• Citrix EdgeSight – http://www.citrix.com/tv/#series/132
• Citrix Workflow Studio – http://www.citrix.com/tv/#series/130
• Citrix Access Gateway Standard Edition – http://www.citrix.com/tv/#series/134
• Citrix Access Gateway Advanced Edition – http://www.citrix.com/tv/#series/140

Introduction

How to create a pool of 2 (or so) XenServers without having to spend thousands of pounds on shared storage?

The simplistic answer is that you don’t need any shared storage in order to create a XenServer Pool, but without it you have export and re-import VMs if you want to “load balance” your XenServers. Of course, the export/import approach is slow, and this is usually the problem that people are trying to solve.

Possible solutions

The “correct way”

Use an Equalogic, NetApp or similar appliance.

In my view this is an “enterprise class” solution is outside the scope of this document.

However, you should use something like this if a) you plan to run a production work load, b) any disk, data or VM loss would be expensive, c) you plan to do any performance measurement.

Advantages

-         Optimum performance with resilience to disk failure.

-         Supported by XenSource, and by hardware manufacturer.

-         This is usually the best solution in the long run.

Disadvantage

-         Initial cost.

OpenFiler “loopback” VM

The idea here is that you install a pre-built OpenFiler appliance VM on some local/un-shared storage on one of your XenServers. As well as a system disk, the OpenFiler VM has an large additional disk that will be used to provide the shared storage. The OpenFiler appliance then shares its large disk using NFS, and the XenServer uses this share to create an NFS based Storage Repository that can be shared.

This approach is fully described in “XenServer_Demo_and_Evaluation_Setup_Guide_v5.5.1″ (CTX118735).

Advantages

-         Other than disk space this is almost a no-cost solution.

-         It is well documented in CTX118735.

-         XenSource make extensive use of OpenFiler servers when testing XenServer.

Disadvantages -

-         This solution is probably the least resilient to failures.

-         Not fast.

-         XenSource do not believe that OpenFiler would handle any significant stress .

-         The OpenFiler VM must be running before any other VMs can start, and in some cases it may be necessary to “repair” the shared SR before other VMs can start.

OpenFiler on a re-purposed PC

This is very similar to the OpenFiler “Loopback” VM (above), but in this case OpenFiler is installed on a physical device such as an old PC or server.

Download Openfiler from http://www.openfiler.com/ and install it on an old PC or server. OpenFiler can then be used to host an NFS server that is suitable use with XenServer.

The installation process is described at http://www.openfiler.com/learn/how-to/graphical-installation, is generally quite straightforward, and should not scare those who fear LINUX.

Configuration of OpenFiler for use with XenServers is probably best described in “XenServer_Demo_and_Evaluation_Setup_Guide_v5.5.1″  (CTX118735).

The cost of SATA disks often makes it worth installing a SATA disk controller card if new or additional disk space is required.

System 3 are currently testing a Dell 380 to host 300Gb of shared storage for a pool of 2 Dell 380 XenServers. No performance data has been taken but the solution has been seen to work.

Advantages

-         It’s easy to set up.

-         A repurposed server, or the inclusion of a RAID card could offer better speed and resilience when compared with an OpenFiler “loopback” VM.

-         XenSource make extensive use of OpenFiler servers for testing XenServer.

-         Less demanding on older hardware

Disadvantages

-         XenSource do not believe that OpenFiler would handle any significant stress.

-         Old hardware may not be reliable or supportable.

FreeNAS

In many ways FreeNAS is similar to OpenFiler in that it is a cut down version of UNIX that has been configured for maximum NAS (Network Attached Storage) performance, and minimum exposure to UNIX.

One respondent who has tried FreeNAS said “… its setup can be completed in 10-15 minutes …. OS footprint is just 64MB, and boot to OS is just a less than 20sec process. The maintenance is almost zero.”

Advantages

-         It’s easy to set up.

-         Less demanding on older hardware.

Disadvantages

-         Old hardware may not be reliable or supportable.

LINUX  on a re-purposed PC

Instead of installing OpenFiler on a re-purposed PC, most people who responded to my request for information used Linux to serve NFS; Ubuntu was the most popular distribution.

Installing Ubuntu is described https://help.ubuntu.com/9.04/installation-guide/i386/index.htmlandhttps://help.ubuntu.com/community/Installation

Installation of NFS on Ubuntu is described herehttps://help.ubuntu.com/community/SettingUpNFSHowTo#Minimalistic%20NFS%20Set%20Up

The cost of SATA disks often makes it worth installing a SATA disk controller card if new or additional disk space is required.

Linux distributions that have been seen to work.

-         Ubuntu with an EXT4 filesystem, serving NFS.

-         Susie with a Razor filesystem, serving NFS.

-         Fedora with an XFS filesystem, serving NFS.

-         In System 3 we use an old Fedora 6 NFS server to provide shared storage to some of our XenServers, and iSCSI for VMware Virtual Infrastructure.

Advantages

-         A repurposed server, or the inclusion of a RAID card could offer better speed and resilience when compared with an OpenFiler “loopback” VM.

-         Of those who responded to my request for information, this was the most popular solution.

-         Depending on your hardware, this maybe the fastest solution for providing shared storage for small XenServer Pools. One respondent has done some performance comparisons using an HP Prolient DL380 (2GB mem) with an HP Smart Array P600 SAS RAID Controller.

-         Ubuntu with an EXT4 filesystem – 225MBps.

-         Susie with a Razor filesystem – Very good.

-         Fedora with an XFS filesystem – Good.

-         Free BSD with a UFS filesystem – Average.

Disadvantages

-         Old hardware may not be reliable or supportable.

-         Some people aren’t comfortable with  Linux

NFS service on a Windows 2008 R2 server.

Windows 2008 R2 now includes an NFS server. It should therefore be possible to host an NFS service on an existing Windows 2008 R2 Server.

In addition to the full graphical version of Windows 2008 R2 Server, there is also the lighter weight Core product which may offer increased performance for a given hardware platform.

NFS services have to be installed separately and the following documents describe how to install and configure NFS on Windows 2008 R2.

http://technet.microsoft.com/en-us/library/cc753302%28WS.10%29.aspx

and on Windows 2008 R2 core

http://blogs.technet.com/jorke/archive/2008/09/10/configuring-nfs-on-windows-server-2008-core.aspx

Advantages

-         Some people feel more comfortable with a Windows solution

-         You may not need any additional hardware as you should be able to add NFS services to an existing Windows 2008 R2 server.

-         Windows 2008 R2 Server may also be used to create shared storage for Hyper-V clusters.

Disadvantages

-         If using old hardware, it may not be reliable or supportable.

StarWind Free iSCSI Target on a Windows.

Another solution that uses a Windows PC or Server is StarWind iSCSI Target. The free version, which supports up to 2 TB, can be downloaded from http://www.starwindsoftware.com/free

“StarWind Free software is provided only for personal use, demoing, training, or test and development and may not be used for commercial or production purposes”.

Advantages

-         Some people feel more comfortable with a Windows solution

-         You may not need any additional hardware as you should be able to add StarWind to an existing Windows PC or Server.

-         StarWind may also be used to create shared storage for Hyper-V clusters.

-         The inclusion of an iSCSI based Storage Repository allows you to enable XenServer’s High Availability option. While you are unlikely to need this in a small XenServer pool, it may be useful if you need to include HA in your testing.

Disadvantages

-         If using old hardware, it may not be reliable or supportable.

-         Some people feel more comfortable with a non-Windows solution

Windows Storage Server 2008

http://www.microsoft.com/windowsserver2008/en/us/wss08.aspx

One respondent has just started using Windows Storage Server 2008 on a Dell T3500.

The primary purpose of this is to provide clustered storage for a Hyper-V / SCVMM development environment, but it may also be an option for XenServer.

Advantages

-         Some people feel more comfortable with a Windows solution

-         Developers and Testers may have a suitable MSDN licenses that would allow them use this solution in a development or test environment.

-         Windows Storage Server may also be used to create shared storage for Hyper-V clusters.

-         The inclusion of an iSCSI based Storage Repository allows you to enable XenServer’s High Availability option. While you are unlikely to need this in a small XenServer pool, it may be useful if you need to include HA in your testing.

Disadvantages

-         Some people feel more comfortable with a non-Windows solution

-         I have no feedback on performance to date.

Other Considerations / Recommendations

-         Make sure that the network between the XenServers and the storage server is as fast as possible. Ideally they should be connected to the same Gigabit switch.

-         Consider putting the storage traffic on a separate “private” network, if you have sufficient NICs in your servers.