When to use mount points for Windows servers

Windows mount points are a common practice in the Exchange world, yet are sometimes misunderstood elsewhere. Here are a few more use cases for mount points.

In my tip about using Windows mount points in lieu of drive letters, a number of readers commented that they had a tough time applying this configuration. Here are several cases where using mount points make sense instead of assigning fixed drive letters:

  • Exchange server database groups: In many large Exchange server configurations, this is a best practice. It is supported for most Exchange configurations, as outlined in this KB article.
  • Windows distributed file system (DFS) shares with many large directories: In this configuration, a folder within a DFS share would correspond to a logical unit number (LUN) on a storage system. This will allow a single DFS share in the Active Directory namespace to have folders that can be managed on a SAN as a single LUN, and not burden the Windows server with too many local disk drive assignments. Further, the DFS share (or the file contents) could be relocated to another server at the SAN controller, saving precious time in large data moves.
  • A means to avoid the use of Windows dynamic disks: In most cases, Windows Server administrators still format drives as basic disk. While the dynamic disk is a way to extend capacity on demand, many administrators keep basic disks in use for application support, consistency, or consequence of default configuration.
  • When working with an application that has a fixed drive letter requirement, yet a dynamic growth requirement: This is sometimes referred to as "fill and spill" for a single drive letter and many folders underneath that drive letter. Each folder would be a mount point, allowing dynamic growth by keeping the same drive letter as a parent identifier.
There are operational considerations to using mount points. The primary point is that the parent drive (which actually has a drive letter) does not report the mount point as a total amount of space for the drive; the used and available space will only show that of the parent drive with the drive letter assigned. Figure A shows a Windows Server 2008 R2 system with three mount points of 1 TB each in the E:\ drive. Figure A

Click the image to enlarge.

In the image, you can see that the three 1 TB drives are assigned as mount points with the name Mount1, Mount2, and Mount3. When viewing the properties of the E:\ drive (the parent for the 1 TB drives), the free and used space is not represented. Further, you can also see the symbolic link represented as a junction point in the command prompt window when doing a DIR command of the E:\ drive. Mount1, Mount2, and Mount3 are the names assigned to the mount points when they were installed.

With mount points, you have a configuration that can scale to large amounts of storage within a single drive letter; this can be especially important if you are receiving the storage from many SAN locations or need to have it contained to a specific drive letter.

If you use mount points, tell us how you use them by posting to the discussion.

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