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When SP1a first came out for Citrix Provisioning Server 5.0 I noticed Citrix slipped in a new feature called Differential Image. A Differential Image is a hybrid of sorts between a Private Image vDisk and a Standard Image vDisk. Simply, it’s a Standard Image with a persistent write cache. The downside is, if the Standard Image is modified the write cache is discarded but the upside is the write cache will survive a reboot. This is great for classrooms and labs in which an end-user needs to be assign a particular machine for a short period of time. But what about for XenApp?
Daniel Feller covers Differential Images in his XenApp Best Practices blog. His only use case is for Differential Images is to allow for additional end-user personalization. Therefore, not need nor recommended for XenApp. I disagree. Another use case for Differential Image is for out-of-cycle updates. That could be software updates, hotfixes, AV signature updates and OS updates. If we use a Standard Image, we are forced to constantly update that image to insure that all of our servers have these updates. If updating images was a sysadmin’s only job then its no big deal. The flipside, if the sysadmin does not keep on top of the images, then AV updates, hotfixes and even new/updated streamed applications will have to be reapplied after every maintenance reboot. By using a Differential Image, a System Administrator can wait a little longer between image updates. Personally, I think using a Differential Image is a better way to deploy XenApp. Not only do you get the benefits of a Standard Image you also gain the flexibility to make out-of-cycle updates. Again, its all relative to organization. Joe
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