Personal vDisk

Personal vDisk

Unlike traditional VDI deployments involving pooled desktops, where users lose their customizations and personal applications when the administrator alters the base VM, deployments using personal vDisks retain those changes. This means administrators can easily and centrally manage their base VMs while providing users with a customized and personalized desktop experience. Personal vDisks provide this separation by redirecting all changes made on a user’s VM to a separate disk (the personal vDisk). The content of the personal vDisk is blended at runtime with the content from the base VM to provide a unified experience. In this way, users can still access applications provisioned by their administrator in the base VM.

Personal vDisks can be used with Provisioning Services or Machine Creation Services. Generally, the use of personal vDisks is evaluated when user groups require the ability to personalize their virtual desktop. This could include a need to use a variety of departmental applications or general personalization that is beyond what is available in the user profile. However, there is no defined limitation of Citrix personal vDisk technology to these specific use cases. It is entirely possible to utilize personal vDisks in scenarios that may not maximize flexibility or virtual desktop density, yet are entirely appropriate to the enterprise environment.

The need and use of personal vDisk technology must align with the personalization characteristics of the user group captured during the assess phase as well as the FlexCast model selected.

Note: Citrix personal vDisk technology loads a set of Kernel mode drivers very early in the Windows boot process. By and large, these Phase 1 drivers allow most applications to work in a seamless manner with a personal vDisk attached. Exceptions to this are applications that operate or install components prior to the loading of the Citrix personal vDisk drivers. Specifically, certain device driver installers or antivirus software may not work properly if installed within the personal vDisk.

Decision: Size

While many factors play a part in deciding the size of a Personal vDisk, there are certain basic requirements that should be followed:

• Minimum size – 3GB
• Maximum size – Undefined

Note: The Personal vDisk can be expanded but cannot be shrunk.
Beyond system requirements, the following major factors influence what size to allocate for a user’s Personal vDisk:

• Anticipated growth – Most organizations should size personal vDisks well above the minimum requirement of 3GB and should factor in each user group’s workload requirement. As a general rule of thumb, the following recommendations provide a good starting point:

Light user – 7GB
Medium user – 10GB
Heavy user – 15GB

• Storage technologies – The use of storage technologies such as thin provisioning and de-duplication can significantly reduce storage requirements for personal vDisks allowing larger sizes to be specified:

Thin provisioning – Administrator can use thin provisioning to present more storage space to the virtual machines than is actually available on the storage repository. De-duplication – Storage requirements may be reduced through the use of data de-duplication, whereby duplicate data is replaced with pointers to a single copy of the original item.

• Folder redirection or cloud data service – In many smaller environments, utilizing personal vDisk as a profile management solution is common. However, the limitations present in distributed profiles quickly present themselves when this option is selected. The first step many organizations utilize towards a robust profile solution is to utilize Microsoft special folder redirection in order to redirect user data to a network share.

Other organizations employ a cloud based data service such as Citrix ShareFile. Personal vDisks can co-exist with either of these deployment options. Depending on the implementation mechanism, the presence of either of these technologies can significantly reduce the initial sizing of personal vDisks for users.

Experience from the Field

Citrix – Analysis of Citrix’s internal deployment of XenDesktop virtual desktops featuring personal vDisk reveal that most vDisks are utilized at a rate of 36.74%. The average size of a PvD is initially 10 GB and has only been expanded for a small number of power users. This size includes user profiles as well as any data, applications and other aspects accumulated in the course of eight months of usage. In this environment that is *NOT* utilizing a profile management solution or roaming profiles, vDisks populate a few GB up front with user profile data then are slowly accreting changes up to the aforementioned level over time.