A few years ago, I wrote a blog on the storage location of ADMX files. For Group Policy, these files are crucial, as they define the settings you see in the Group Policy Editor, and by extension, they describe the registry settings which need to be managed on each client workstation to which a policy is applied.
(Contrary to popular belief, the Group Policy Engine on a client does *not* need to refer to these files to actually apply Group Policy. The Group Policy Editor parses the file and stores the specific registry modifications in the appropriate location in the SYSVOL folder structure. The editor does, however, require access to all the proper ADMX files to allow an administrator to make policy changes)
The ADMX format was introduced in Windows Server 2008 and Windows Vista and is XML-based, unlike the previous ADM file syntax of Windows Server 2003, which was a custom syntax which proved challenging at times.
In my earlier post, I specified that the best location to store these files is %systemroot%\PolicyDefinitions on each of your DCs. This was in response to a specific problem I had at a customer with a new, single, standalone Domain Controller.
However, on much larger networks, this advice is not something I would endorse. By storing the policies in the PolicyDefinitions container on each DC, the ADMX files will only be available in the Group Policy Editor on that particular Domain Controller. If you want to use Group Policy Management Console from a workstation, another DC or a member server, then you are going to have many settings which have no policy definition, so you will be unable to manage them. With products like Server Core (a particular focus of Windows Server 8 Beta), managing Group Policy from the DC’s desktop is no longer a recommended or particular routine operation. Similarly, managing a DC directly from its desktop for such routine changes is not a best practice – delegating control over Group Policy and making the changes on a workstation would be a better choice. So, we need a better way of sharing the ADMX files across the entire LAN to ensure they roam to any machine where policy may be set.
Fortunately, Microsoft already have a solution. It’s known as the Central Store. Essentially, this is a PolicyDefinitions folder within the SYSVOL folder hierarchy which you already know about. By placing the ADMX files in this directory, they are replicated to every DC in the domain; by extension, the ADMX-aware Group Policy Management Console in Windows Vista, Windows 7, Windows Server 2008 and R2 can check this folder as an additional source of ADMX files, and will report them accordingly when setting your policies.
By default, the folder is not created. Whether you are a single DC or several thousand, I would strongly recommend you create a Central Store and start using it for all your ADMX file storage. It really does work well.
More information and detailed procedures are available from Microsoft Support.