Standard Image mode allows multiple target devices to stream from a single vDisk image at the same time; reducing the amount of vDisk management and reducing storage requirements.
When a vDisk is configured to use Standard Image mode, it is set to read-only mode. Each target device then builds a write cache to store any writes the operating system needs to make. There are several write-cache options available. Because the vDisk is read-only, each time a target device boots, it always boots from a ‘clean’ vDisk. If a machine becomes infected with a virus or spyware, the target device only needs to reboot the image.
When updates are made to a vDisk in Standard Image mode, changes against the base vDisk image are captured in a differencing disk file (.aVHD), resulting in a new version of the base image. Each new version remains directly associated with the base image. Versioning allows for the updates captured in the differencing disk to be staged (Maintenance, Test, Production) before those changes become available to Production devices. If issues are encountered with a version, that version can simply be reverted. For details on versioning, refer to Updating vDisks.
While each target device is using the same vDisk, Provisioning Services personalizes the streamed image for each target device, providing the information needed to ensure the device is uniquely identifiable on the network. In addition, the product provides a mechanism to specify additional personality settings for each device. This feature allows you to store application specific values in the database and retrieve the target device’s unique value as the device loads. For more details, refer to Managing Target Device Personality.
A vDisk that is in Private image mode closely models how a computer uses a regular hard drive. That is, only one target device can use a Private Image vDisk at a time.
The following illustrates Private Image vDisks (read/write) that are each assigned to a single Production device, and a Standard Image vDisk (read-only) that is assigned to and shared by a collection of Production devices. For Standard Image vDisks, write cache options include cache on server disk, on a devices hard disk drive, or in the devices RAM.