We have two vDisk modes:

• Standard Image – Select this mode if a vDisk is shared by multiple target devices (write-cache options enabled).
• Private Image – Select this mode if a vDisk is only used by a single target device (read/write access is enabled).

Standard Image mode

Standard Image mode allows multiple target devices to stream from a single vDisk image at the same time. This mode reduces the amount of vDisk management and reduces 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 (.Avhdx), 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.

Although each target device uses the same vDisk, Provisioning Services personalizes the streamed image for each target device. PVS provides the information needed to ensure the device is uniquely identifiable on the network. You can also specify more personality settings for each device: you can 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.

Private image mode

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. All the updates/changes made to that vDisk is written directly to the disk.