The Magic of Mount Points

For UNIX users, the concept of mount points is old hat—something that UNIX and other OSs, such as Novell NetWare, have used for years. However, in the Windows space, mount points are a relatively new concept. Let's look at how Windows uses mount points and the value and usefulness that this minor but powerful feature provides for Windows Server 2003 and Windows 2000 Server storage systems.

A Brief Mount Points Primer
The idea of mount points, which originated in UNIX and older minicomputer OSs years ago, grew out of a desire to simplify storage management. Simply put, a mount point is a physical location in the directory structure on which you graft—or mount—the root directory of another volume. Mount points are persistent directories that point to disk volumes; in Windows, they always resolve to the root directory of the desired volume. Because mount points don't require that you associate each disk volume with a drive letter, they overcome Windows' drive-letter limitation (i.e., only 26 drives—A through Z) for disk drives.

When you use NFS to mount a remote file system, you must specify both the remote resource name and the local file-system location for that resource. In Windows, you must use an NTFS directory to host the volume mount point because the underlying mechanism uses NTFS reparse points. You can mount a variety of file systems, such as CD-ROM File System (CDFS), FAT, FAT32, NTFS, and Universal Disc File System (UDFS).

Mount points provide a useful storage-management tool that avoids the tedious work of assigning specific volume mappings to every disk resource (whether local or remote). Integrating local and remote disk resources into a unified and singular directory tree greatly simplifies file-system traversal and makes the traversal transparent to the administrator, application, and user.

Using Mount Points in Windows
Administrators of non-Windows systems understand mount points and use them extensively, but Windows administrators are just beginning to realize their power. Because the Windows storage-management paradigm has always relied heavily on alphabetic drive-letter designations, mount points—with their lack of dependence on drive-letter associations—are especially valuable. When Windows servers were simple and rarely assigned more than 5 or 10 drive letters, the need for mount points was almost nonexistent. Today, however, the need for mount points has become vital because Windows administrators are building larger, more complex servers that have numerous attached storage solutions, such as Network Attached Storage (NAS) devices and Storage Area Network (SAN) devices. Add complex applications such as Microsoft Exchange Server and Microsoft SQL Server to the mix, and drive-letter scarcity becomes even more of a problem. Clustering further complicates the situation because an entire cluster is allowed only 26 drive letters. (A shared disk resource in a cluster must maintain a consistent drive letter regardless of which cluster node owns it.) Microsoft added volume mount points to Windows 2003 and Win2K Server to overcome these problems with drive-letter limitations and to simplify storage management.

You can configure mount points on Windows three ways. The first method is perhaps the most familiar to Windows administrators. You use the Microsoft Management Console (MMC) Disk Management snap-in (diskmgmt.msc) to mount volumes to already-configured physical drive resources by selecting Add Mountpoint from the interface. Second, if you prefer to use the command-line interface, you can run mountvol.exe from the command line. Third, you can use Win32 API calls in your own .exe file. Win32 API's SetVolumeMountPoint and DeleteVolumeMountPoint functions add and delete mount points, respectively.

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