Friday, September 23, 2011

XenDesktop MCS updating master


If you are using the Machine Creation Services (MCS) to created dedicated images, this does not really matter, but if you update the master and want to mint more VMs in the same catalogue (without affecting the current). This is how it works.

The MCS in XenDesktop 5.5 is pointed to a master image when a Catalogue is created. You can be pooled or dedicated:

  • Dedicated virtual desktops retain all changes, software installations, local data, in a local difference disk.
  • Pooled Catalogue virtual desktops do not retain changes, the difference disk is reset upon reboot.

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 centralised patch and application management. Each deployed image, whether pooled or dedicated, will also contain an identity disk.

Master Image - Once a master image is identified (when the catalogue is created), a private-use clone of the VMDK is created for use by all the catalogue machines.

This cloned disk is separate from the Master Image VM, allowing that VM to be updated or deleted with no impact on the deployed virtual desktops.

This master image clone is copied to each VMware Data-store automatically.

Each catalogue is linked to its own master image clone. If multiple catalogues are defined, then multiple master clones will be generated.

A master image can be changed to a different disk using the following command in PowerShell: Publish-ProvMasterVmImage. This will only impact new machines created in the catalogue, not existing machines already generated.

I hope this helps explain the disks under the covers.

image

Sources:
http://forums.citrix.com/thread.jspa?messageID=1534982
http://www.thegenerationv.com/2011/03/xendesktop-5-deep-dive-machine-creation.html

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