Microsoft’s DFS can be used to organize SMB (CiFS) file shares into a virtualized file namespace. Creating a DFS namespace decouples end user data access paths from the physical locations of the storage, providing storage administrators with considerable flexibility in managing their storage devices.
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A DFS namespace consists of a DFS root, which is a special type of file share, and a collection of links, which are paths that resolve to the DFS root. A DFS link redirects the DFS client to the physical location of the storage. The DFS client is included in the Windows codebase and it automatically runs on a user’s system whenever it accesses a DFS namespace.
DFS namespaces come in two basic flavors: stand-alone and domain-based. A stand-alone DFS namespace is hosted on a single server and is accessed directly on that server. A domain-based DFS namespace is contained in an Active Directory server; the namespace is hosted on one or more servers in the domain and is accessed using the domain name.
For example, if the stand-alone DFS namespace is hosted by the Windows server “MyServer” and the DFS root share name is “DfsRoot”, then a link in the namespace is a UNC path of the form \\MyServer\DfsRoot\Link1. Note that the namespace path can contain intermediate subdirectories, so the link might also be something like \\MyServer\DfsRoot\Subdir1\Link1.
As an example with a domain-based DFS namespace, if the domain name is “MyDomain.local” and the DFS root share name is “DfsRoot”, then a link in the domain-based DFS namespace is a UNC path of the form \\MyDomain.local\DfsRoot\Link1 or \\MyDomain.local\DfsRoot\Subdir1\Link1.
When a user accesses a DFS root, by typing the root’s UNC path in Windows Explorer, the user sees the root-level links and folders in the DFS namespace. When the user opens a folder in the DFS namespace, he sees the links and sub-folders contained in the folder. When the user opens a link in the DFS namespace, the DFS client on his machine receives a list of one or more link targets from the DFS server. The list of link targets is called the link referral, and each target in the referral is a UNC path. The DFS client selects one of the link targets and redirects the user to the specified UNC path.
The acts of getting the DFS link referral, selecting a link target, and redirecting to the UNC path of the link target are all transparent to the user. The user simply sees the DFS link path in the Windows Explorer address bar, and sees the contents of the target file share in the Windows Explorer details pane.