Recipe 7.13. Creating a Virtual Drive to Another Drive or Folder

Problem

You want to make a folder the root of a drive or you want to use multiple drive letters for the same drive.

Solution

Using a command-line interface

Use the following command to create a new drive pointing to an existing path on the system:

> subst <Drive> <Path>

The following example creates an E drive pointing to C:\scripts:

> subst E: C:\scripts

The following example creates an F drive pointing to C:

> subst F: C:\

Using VBScript

There aren't any WMI or WSH interfaces for creating virtual drives, but you can shell out to the subst command if you really want to do it via a script.

' This code creates a virtual drive. ' ------ SCRIPT CONFIGURATION ------ strDrive = "<Drive>"  ' e.g. e: strPath  = "<Path>"   ' e.g. c:\scripts ' This assumes subst is in your PATH, if not, fully qualify ' the path to the command here: strCommand = "subst " & strDrive & " " & strPath ' ------ END CONFIGURATION --------- set objWshShell = WScript.CreateObject("WScript.Shell") intRC = objWshShell.Run(strCommand, 0, TRUE) if intRC <> 0 then    WScript.Echo "Error returned from running the command: " & intRC    WScript.Echo "Command attempted: " & strCommand  else    WScript.Echo "Command executed successfully." end if

Discussion

The subst command is a useful utility for making folders on a volume appear as a drive. Let's say, for example, that you like to store files in your user profile (e.g., C:\Documents and Settings\rallen\My Documents\scripts) and need to frequently access those files from a command line. You are starting to get carpal tunnel syndrome because even with tab-completion enabled, it takes a bit of wrist work to type out that path. You can use subst to create a drive that is mapped to that folder path and save yourself a lot of typing.

There are a few caveats to be aware of when using subst:

The drives are removed after reboot: Perhaps the biggest drawback to virtual drives is that they are removed when a machine restarts. That means to create a persistent virtual drive you need to use a logon script.
Shadow copies are not created: On Windows XP, shadow copies are created for all local volumes, but this doesn't apply to virtual drives created with subst. Since the virtual drive corresponds to a logical volume, a shadow copy is already created for its contents.
The drives cannot be used to set quotas: Again, due to the fact the contents of a virtual drive are already part of a volume, which may already have quotas enabled, you cannot configure quotas.
Deleting the virtual drive deletes only the mapping, not the data: If you delete a virtual drive using the /d option, only the drive mapping is deleted, not the underlying contents of the drive.