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XenApp Version 6.5 – Session Launch Issues with VMware EVC

There is a confirmed issue with XenApp 6.5 when running on a VMware Cluster where EVC is turned on.

EVC in VMware is a compatibility feature in an ESX cluster used to migrate virtual machines between ESX hosts that are not 100% identical.  When this is enabled some of the CPU features are not used as the host configure a common CPU for the VMs to utilize,  this feature however causes certain XenApp 6.5 sessions to disappear after a session is started.  According to Citrix, disabling EVC corrects the issue.

After doing further investigation, Citrix confirmed the issue is resolved by turning EVC off on your ESX cluster (Ouch!)

This does present a BIG issue as servers in a VMware cluster are most of the time not identical.

The options:

  1. Turn off EVC on your cluster (if you are able to) – EVC settings do not take effect on a VM unless the VM is powered off and then powered on (a reboot is not sufficient). As such, any features you may gain after disabling EVC will not take effect until the VM is powered off and then back on.
  2. Configure the LogoffCheckerStartupDelayInSeconds reg key on servers. Citrix confirmed that setting this key appeared to improve things. However as more users opened sessions the problem may continue.

This issue occurs in the following scenarios:

  • The Citrix Policy Client USB Plug and Play Device redirection is enabled, as shown in the following screenshot:
    Note
    : The users do not experience issues, if the Prohibited option is selected.

  • To resolve the preceding issue, complete the following procedure:
  • Create the following registry key,
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Citrix\wfshell\TWI
    DWord (32bit) – LogoffCheckerStartupDelayInSeconds
  • Set the value of the key as 10.
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About CyberRuiz
Highly motivated with over 12 years experience on Citrix/VMWare/Microsoft/technologies. Exceptional communication skills and team player. CCIA – Citrix Certified Integration Architect. CCEA – Citrix Certified Enterprise Administrator. VCP – VMWare Certified Professional in ESX 2.x, VI3, VI4 MCSE – Microsoft Certified Systems Engineer

2 Responses to XenApp Version 6.5 – Session Launch Issues with VMware EVC

  1. Citrix Guru says:

    This is insane… I thought I was the only one that was experiencing issues. Funny enough we always set our ESX clusters with EVC as we know in the future different CPU boxes will show up. I am really curious how Citrix will handle the situation. Many enterprise shops are running VMware. Thanks for the post, this is a HUGE red flag. Perhaps you can include where you found this info. Will help me present this to Management and show them actual Citrix documentation with the issue.

    • CyberRuiz says:

      Tell me about it Citrix Guru… I always tend to lean towards physical servers when deploying XenApp. However as you know virtualization is so much easier to manage.
      I am currently working on a big deployment and started seeing the issue appear every now and then. After spending some time reading forums and googling around, I found these 2 CTX articles.
      http://support.citrix.com/article/CTX131628/ and http://support.citrix.com/article/CTX128953 which officially describes the issue.

      Trying to get more info from Citrix Support, to see if this is specific to an ESX version. Since vSphere 5 handles the CPU masking a bit different, I am not sure if the issue will still occur. At the moment, I am seeing this with ESX 4.x…

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