When a Machine Creation Service (MCS) catalog is created in XenDesktop 7.5 or XenApp 7.5 using VMWare vSphere 5.0 the machines that are created might not be isolated correctly from the master image that was used to create the catalog. No other combinations of XenDesktop/XenApp and VMware are affected.

Normally when an MCS catalog is created, a full copy of the master image snapshot is taken and copied to all storage locations. In this error case only a delta to the parent snapshot is copied to all storage locations. This means that a fully copy is not made and the file deployed to all storage locations is still linked to the original Virtual Machine (VM) and snapshot.

The consequences of this is that if parent of the originally selected snapshot is removed or if the Master VM is deleted, the machines created stop working and do not boot. Also, as the created VMs are linked to the original VM disk, the read IOPS might come from the storage that the master VM is located on, not the storages that were selected in the Resources/hosting unit causing unexpected load on that storage that the Master VM is located on.

Detecting if MCS created machines are affected

Upgrade to XenDesktop or XenApp 7.6, or a later version. In Citrix Studio, select a Machine Catalog node, select the catalog to be tested then select the Test Catalog option. Any machines in that catalog that are affected by this issue will be shown in the test results.

To resolve the issue, complete the following instructions:

1. Upgrade to XenDesktop or XenApp 7.6, or a later version, depending on the type of catalog you have.

   1. Pool​ed (either Random assignment or PVD static) catalog
      Perform an image update on the catalog affected. The selected snapshot can be the same snapshot that was used to create the catalog.
      When this update is complete, the updated catalog will be isolated from the snapshot correctly.

   2. Dedicated catalog
      Contact Citrix Support to get help for this issue.