A virtual desktop analogy: Part two – The private property

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In part one, I discussed how a stateless desktop is like a hotel. In this part, I am going to discuss how a dedicated desktop is like a private property.

Properties built from a common blue print, also offering custom built “executive” houses. Even if they are built from a common blue-print, tenants can and will customize them over time in any way they want, over time they will become unique.

Tenant’s View (user):

• The properties (dedicated desktops) are already equipped with common facilities (applications) and the tenant can install any additional ones they would like.

• The tenant owns the property, they will personalize every aspect of the house and permanently store personal items anywhere in the property (personal data anywhere in the image).

Property Manager’s View (IT administrator):

• Build and Maintenance Effort: High, any custom build will require additional design effort (image). Even if the initial build is from a common blue-print the property becomes unique over time anyway. Maintaining and supporting these additional facilities (applications) as well as controlling compliance with property regulations increases cost significantly.

• Utilization: The property is yours, if you are not using it, no on else can, it will remain empty (desktop unused), no over subscription is possible.

• Availability Requirements: Very High, if your property becomes unavailable due to scheduled maintenance or unforeseen issues the tenant is ‘homeless’. In the event that your home itself (your desktop) gets destroyed it would have to be rebuild from scratch (assuming your property manager maintains updated “build plans” of your ever changing property (image backups) – all driving up the maintenance cost for your property significantly. If the infrastructure (e.g. electricity) running your private property fails (host failure) the property will be unusable unless it has been build with redundant/ shared facilities that can take over and run your property instead (host level failover using shared storage) – again, driving up cost massively. There is inherent dependency between the tenant and the property (user and his/her desktop image).

• Reality is that the tenant will probably check into a ‘hotel’ at this point
So while the tenant or better desktop user, will appreciate the potentially unlimited level of personalization and upgrade of functionality, this scenario is a nightmare for the IT organization.

Maintenance of a large number of unique images requires careful backup and availability planning, maintaining the additional applications (or correcting issues they can cause) will result in significant administrative overhead compared to stateless images.
The infrastructure required to run these highly available images will drive up cost significantly – specifically through a drastic increase in shared storage requirements.
The private property approach is however the one we are used to (who wants to live in a hotel?) … and for VDI users with specific requirements or simply executives who want maximum functionality whatever the cost a dedicated desktop has its place. We often see hybrid deployments and the key to success (reducing cost) is a careful user categorization and analysis of functional requirements to increase the share of stateless desktops in your environment.

We have seen “layering” technologies becoming mainstream that blend the two approaches. They have been around for some time as point solutions like Unidesk but are increasingly integrated into the vendor apartments with Citrix’s personal vDisk being a great example.

Imagine you are in a hotel that provides the futuristic feature of a “floating” personal room that can be detached and magically attached to any of the apartments.

The tenant is allowed to store any personal items and even install the above mentioned home cinema system (or any other personal applications) in this “floating personal room” (personal vDisk).

When the user moves between apartments the personal room will be detached and reattached to the new apartment retaining the personalization and functionality that it provides over and above the standard apartment even if the apartment was cleaned or refurbished (image reset or recomposed).

If you are familiar with VMware View’s “persistent disk” or Verde’s “user disk” implementation you know that this personal “room” exists today but can only be used to store your suitcase items (profile) and items you’d have put into hotel storage (my documents etc.) surviving a clean of the apartment or even a refurbishment (reset or recomposing of the image). If you however decided to install the above home cinema system (personal application) in this room it would be there after the apartment was cleaned/refurbished but it would not function anymore.


Well, the installation of these applications also make changes to the base image (think of it installing a power junction in the standard hotel apartment (not your personal room) to power your home cinema system. There is no intelligence that tracks the dependencies and changes and when you try to reattach the magic floating room to a new apartment the required power junction is simply not there. So the home cinema system is still physically in your room but won’t function.

This is where the beauty of the personal vDisk comes into play.

When using the personal vDisk a filter driver in the image will track all changes and ensure that they are routed to your “personal room” and more importantly that they continue to exist in isolation from the base image (think of it as installing a duplicate power supply in the floating room rather than utilizing the existing one in the apartment).

The result is a model that preserves the best of both approaches in the VDI world, a stateless base image (with all the associated benefits) combined with a ‘layer” (room) of personal applications and customizations (requiring only those to be highly available and backed up rather than the entire image).

Even the personal vDisk has limitations today where in reality it does not float automatically between desktops (following the user) but is associated with the desktop and needs to be manually reattached to the new “hotel apartment” by the administrator in recovery situations – but we are halfway there and other vendors work on similar functionality (VMware’s Horizon Mirage).

It’s just a question of time and, well, inventing floating hotel rooms.

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