I will get the discussion started.
So, on the surface, OS X Server has a number of features to allow you to unify the two locations. Let's make some assumptions. First, you will have a firewall installed at each location that allows persistent site to site VPN. Now, you have one large network in two physical locations. This means that users in site A can access resources in site B and vice versa. Ok, that takes care of the network. That is outside OS X. Next, the user domain. Open Directory supports master and replica structures. You can define one server to be the domain master and another (or more) to be a replica (or replica of a replica). Now, you have a centralized location for users, groups, passwords, policy, etc. This is all built on a solid DNS infrastructure which also supports master/slave configuration.
Ah, so on the surface, this means that users can move between locations and use the same core domain services. But, you hint at the ability to "Staff can use any machine and would be expected to travel between the two offices." This presents an interesting challenge. In OD, a user can be assigned a network home folder, allowing the user to use any machine and access a home folder from a network location. This allows the user to access any machine and always have access to her data. Ah, but OD defines the home folder as a single value. So, user Ian might have a home folder pointing to serverone.gurdon.com. But is serverone is in location A and user Ian goes to location B, his login time will be really slow since he needs to traverse the ADSL line to access his data. Basically, it will be unusable.
So, perhaps a better solution is to not link the servers via OD but to create exact copies on both sides and only sync the data. Here is my thinking on this.
Site A:
Server named sitea.gurdon.com
Users: John with UID 1026, Mary with UID 1027, Bobby with UID 1028, and Sue with UID 1029
Users all setup to access a local network home share on sitea.gurdon.com, allowing John, Mary, Bobby, and Sue to move access their home from any system.
Site B:
Server named siteb.gurdon.com
Users: John with UID 1026, Mary with UID 1027, Bobby with UID 1028, and Sue with UID 1029
sers all setup to access a local network home share on siteb.gurdon.com, allowing John, Mary, Bobby, and Sue to move access their home from any system.
In the background:
You use a synchronization product to two way sync user data between the two locations. As long as your UID/GUID values are the same, then the two systems will run independent of each other as two distinct yet matching OD servers. To sync the data, look at something like File Replication Pro, GoodSync, or rsync. Depending on the user behavior, you might be able to do a nighty sync instead of a live sync as the assumption will be that users will spend a full day at one location and not move between locations within a workday. That ADSL is you roadblock.
Ah, now the pieces of this that will make it all fall apart is the mention of " user data consists of documents and larger video files." Network home folders and video workflows is like oil and water. Generally it is something you can setup but the experience is a goopy mess.
Now, there is also the possibility of products like DropBox, allowing user data to cache to a cloud solution. Or, perhaps you centralize you work on the file server and then just sync file server data, allow the clients to be thin. If you go with network home folders you must be at minimum on a 1000Base network. I recommend the server be link aggregated or you move to 10gigE.
I think the overall statement is that this is a problem that has a solution. However, more details about your workflow are required to fully expose the best possible solution.
Hope this helps with the thinking process.
Reid
Apple Consultants Network
Author - "El Capitan Server – Foundation Services"
Author - "El Capitan Server – Control & Collaboration"
Author - "El Capitan Server – Advanced Services"
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