Eyes glaze over, the meaningless automatic nodding starts and you can feel the person’s mind is miles away … yes, I admit, I had several such fruitless attempts of explaining the concept and benefits of using ‘stateless versus dedicated desktops’.
Stateless desktops are often also referred to as ‘non-persistent’, ‘pooled’ and ‘dynamic’ and dedicated desktops as “persistent” or “private”.
Actually its simple – a stateless desktop is to the IT Administrator what a hotel room is to a property manager.
- Hotel apartments (stateless desktops)
- Residential area with private properties (dedicated desktops)
Hotel: (stateless desktop)
- Tenant checks into the hotel and get any available apartment (desktop) allocated.
- On check-in the tenant typically brings their suitcase (user profile) that they use to populate or customize the apartment with personal things they need or like while in it.
- They use it for a period of time, will check out when not needed which means all personal belongings will taken away and stored in their suitcase for the next visit.
- The apartment will be cleaned (“reset”) so that the next tenant finds it “as new” (changes to the desktop will be discarded; making the desktop itself “stateless”)
- The apartment will then be made available to any other potential tenant.
- The next time our tenant checks into the hotel he/she will (most likely) get a totally different apartment (remember … desktop) and won’t care as long as it provides the same functionality.
Tenant’s View (user):
- Functionality: Good, as the apartments are equipped with all the facilities and appliances commonly required e.g. kitchen, bathroom etc (MS office, Mail applications etc. built into the Golden image)
- Personalization: Typically adequate, the level of personalization varies – depending on how big your suitcase is and what you are allowed to bring, the hotel chain would provide centralized storage for permanent personal items outside your apartment or hotel (network drives, folder redirection), some even provide the equivalent of a personal designer service that allows for advanced customization of your apartment to make it really feel like yours (advanced profile management software like AppSense, RES etc).
- Major functionality upgrades: The hotel will obviously not allow you to buy a personal home cinema system (your favourite PC game) and permanently install it in the hotel apartment. You could … but be assured that it won’t be there next time you check in (remember, you’ll check into a different room and changes you make to the apartment get cleaned up anyway).The hotel could however provide custom services (applications) through alternative methods if required, think of it as ‘room service’ without having to install a kitchen (e.g. application streaming or XenApp publishing).
Property Manager’s View (IT administrator):
- Build and Maintenence Effort: Low, a collection of standard “cookie cutter” apartments from a common blue-print (golden image) NB: I’ll avoid the delta disk/Linked Clone analogy. A common set of furniture and appliances (apps) can be maintained across all apartments. For any custom services like room service to complement the base functionality, additional facilities (cost) are required but can be handled centralized (e.g. streamed apps).
- Availability Requirements: Low, If a apartment becomes unavailable due to scheduled maintenance or unforeseen problems (flooded bath = image corrupted through user error) the tenant can simply check out and check in to another apartment (connects to another desktop). There is no dependency between the tenant and a apartment (user and desktop image).Even if the entire hotel experiences a power cut (host failure) with all apartments becoming unusable, the tenant can simply check into a apartment in another hotel as long as total capacity across all hotels is sufficient.
- Utilization: The apartments can be oversubscribed (need to accommodate number of concurrent tenants only)
The stateless desktop allows the administrator to build desktops from a common image base that is easily deployed and maintained, the stateless desktop itself does not need to be made highly available and can easily be replaced with another available desktop if the desktop (or host) becomes unavailable.
In Contrast – Private Properties (Dedicated Desktops):
- Properties build 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) :
- Functionality and major upgrades: “unlimited”, the apartments are already equipped with common facilities (applications) and the tenant can install any additional ones they would like.
- Personalization: Great, 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 😉
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.
We have seen technologies becoming mainstream that blend the 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).
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).
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