I run a small start-up with 3 people working in 3 workstations (running Windows Vista/7) and a server running Windows Server 2008. Oh, I almost forgot... we also have a linux server (inside a VM hosted in the Windows Server 2008 server).
As we are just a few people with just a few nodes, we use a workgroup network model to avoid the configuration burden of a domain model.
- Is the workgroup model right for us?
- Should the number of users/nodes be the only factor to consider? I guess not. So, what other factos should we consider?
- If those other factos point to a workgroup model, but the network becomes to big. How big should it be (in terms of users and nodes) in order to migrate to a domain model an take advantage of its benefits?
Using a domain makes many things easier (authentication and authorization to shared resources) but requires a certain amount of knowledge. I would recommend you do not set up a domain until you're prepared to have two servers dedicated to the Domain Controller role (no other roles and not hosted VMs). These don't need to be huge servers; single processor, 4GB RAM and a small RAID 1 will be more than sufficient. Setting up a domain also depends on how you're connected to the internet, if at all.
Just off the cuff I'd say it would be helpful to migrate to a domain once you have 10 nodes or multiple users per node. A domain would also be very helpful/required if you decide to host your own e-mail server.
For 3 computers? Sure, I might have looked at using a Linux box or Windows Home Server instead of Server 2008 to save on licensing costs, but for 3 users the need for a domain is most likely very low.
The number of users matters only indirectly. Usually you want a domain, when you need features you can only use with domain. Like Group Policies, Exchange, and so on. Lots of windows server functionality and MS Servers only work well in a domain environment. But for a really small number of users it is very rare to actually need those features.
You will want to switch to a domain when you need to use a feature that can only be used on a domain. If you want some redundancy for that 2008 server you will want a domain. If you want Exchange you will want a domain. If you want users to be able to work from any computer instead of an assigned you may need a domain.
If you think you will be growing a lot, or think you will need some feature that only works in a domain in the future you may want to enable a domain now to save having to change things on your computers later.
If security, auditing and object tracking become a concerning issue then switch to the domain model. If sharing object resources such as files/folders/printers are potentially expanding over time there is another benefit of the domain model (active directory). It does not hurt to start now however keep in mind having only one windows 2008 server as your only domain controller brings up concerning issues about redundancy.
you dont want your windows 2008 server be a single point of failure, with that in mind you would probably want to have 2 of them and this will provide a level of reassurance behind the technology.
keep in mind if you are not comfortable with administrator of active directory it may add a level of complexity although the good thing about AD is it runs itself aside from general creation of new users and objects.
having to upgrade to a domain model later might be an issue depending how many machines join in on the network and the location/resources of your file servers.