Machine Creation Services (MCS) is one option for desktop image delivery. It simply uses the hypervisor APIs (XenServer, Hyper-V, and vSphere) to create, start, stop, and delete virtual machines.
When XenDesktop Desktop Studio is configured, a hosting infrastructure and storage system is defined. This hosting infrastructure can be Citrix XenSerspver, VMWare ESX/vSphere, or Microsoft Hyper-V. Storage for use by XenDesktop is also defined, which can be local storage or shared storage. In a production vSphere environment, shared storage defined as VMWare Datastores is preferred.
When using Machine Creation Services (MCS) in XenDesktop 5 Desktop Studio, a Master Image is identified when a Catalog is created. MCS Catalogs can be designed for Dedicated or Pooled virtual desktops. Pooled Assignments can be set for static assignment or random access.
Dedicated Catalog virtual desktops retain all changes, including software installations and local data, in a local difference disk. Pooled Catalog virtual desktops do not retain changes, the difference disk is reset upon reboot, leaving only a copy of the master image. However, when using pooled desktops, the base image can be updated allowing changes from the master disk to be replicated to the deployed VMs, providing for centralized patch and application management. Each deployed image, whether pooled or dedicated, will also contain an identity disk; all deployments utilize thin provisioning.
The following chart highlights the benefits of each type of XenDesktop Catalog:
Graphic taken from Xendesktop 5 Reference Architecture