Tips and tricks - Managing drive letters


The drive letter of an external USB drive changed or keeps changing.

Possible ERROR message: Backup drive(s) not found.



If an external USB hard drive is being connected to a PC, the next free drive letter (e.g. "E") is automatically being assigned to that hard disk by Windows. If the hard disk is then disconnected, e.g. after a backup was performed, and other USB devices and hard disks were connected in the meantime, then the original assigned drive letter (e.g. "E") may be reassigned to another device.


Reconnecting the backup drive e.g. to the same or another USB port may then lead to a new drive letter (e.g. "G") to be assigned to the backup drive. This is the case when another USB drive or stick is still connected and occupies the previous drive letter (e.g. "E") or when another USB port is being used to connect the backup drive.


However, the existing TMS Stein's Backup configuration still expects the original drive letter "E" (in this example) in the TARGET drive and path hence throwing out the above error message "ERROR - Backup drive(s) not found".


Solution (general)

  • Assign a fixed drive letter to the USB hard drive which is to be used for the backups. It is recommended to use a drive letter from the higher end of the alphabet such as X, Y or Z. This will allow other temporary drives to be filled in consecutively from below.
  • The following approaches may be used depending on the current system and backup setup (scenarios) by either using Windows own functionality or by using the USB Drive Letter Manager (USBDLM) developed by Uwe Sieber.

Solution - 1 -

Assign drive letter using Windows own functionality


Scenario 1:

A single and only the same external USB drive is always to be used as a backup drive.

This is the easiest and quickest way if the above conditions are met. If more drives have to be used and swapped or rotated see Solution - 2 further down.


How to change and assign a fixed drive letter: Windows 7

  • Click on Start;
  • Click on Control Panel;
  • Click on System and Security;
  • Then click on Administrative Tools;
  • The next step will require administrator rights so best way is to
    Right-mouse-click on Computer Management and then select Run as administrator and enter the password if requested (my preferred option);
  • In the left pane, click Disk Management;
  • Then right-mouse-click on the drive that needs to be change, and then select Change Drive Letter and Paths from the context menu;
  • Click Change;
  • Click Assign the following drive letter;
  • Select the letter that shall be used in future;
  • Click OK.

How to change and assign a fixed drive letter: Windows XP

Solution - 2 -

Assign drive letter(s) using the USB Drive Letter Manager (USBDLM)


The USB Drive Letter Manager (USBDLM) was developed by Uwe Sieber. Thanks to Uwe Sieber for this excellent product!


USBDLM - Overview

USBDLM is a Windows program which runs as a service and which gives control over Windows' drive letter assignment for USB drives. USBDLM is a program developed by Uwe Sieber and it is NOT part of the TMS Stein's Backup (Pro) package. However, it provides very useful configuration options in respect to USB drive letter handling and hence is a very useful tool to be used in conjunction with the backup program when USB drives are used as backup media.


Please note that while USBDLM is freeware for private and educational (schools, colleges, universities) users, one licence per computer is required for all other users after a 30 day test period even though the software does not expire.


Please refer to Uwe Sieber's USBDLM website for fully-fledged descriptions, help files and downloads.


The brief step-by-step instructions below are only tailored to the outlined specific conditions and should not replace the help file. Please consult the programs detailed help files for additional in-depth reading and a full description of all the functionality provided by USBDLM.


I have found that this solutions works very well for all the scenarios (1 to 3) described here and is recommended especially if the Scenarios 2 and 3 apply.


Scenario 1:

A single and only the same external USB drive is always to be used as a backup drive.

This is the same scenario as described as Scenario 1 under Solution 1.


Download and installation

  • Download the latest USBDLM installation zip file from the software website below and place it into a temporary directory. Make sure the right 32bit or 64bit version is being picked.
  • Unpack the zip file which automatically places all file into the USBDLM subdirectory.
  • Create a USBDLM program directory on the system partition. NOTE: As to program specifics the author of USBDLM recommends NOT to use the default Windows programs directory under Vista and Windows 7 ! I personally use C:\programs\usbdlm_64\
  • Copy all the unzipped files from the above USBDLM into e.g. C:\programs\usbdlm_64\ . Administrator rights may be required.

Configuration (on the system)

  • Most of the installation and configuration steps described below will required administrator rights. USBDLM comes with a set of helper script/batch files aiding the installation and configuration. It is strongly recommended to use these scripts as they will call the USBDLM.exe with the right command line params etc. and also request the required administrator password. The scripts provided are "_edit-ini.cmd", "_install.cmd", "_start.cmd", "_stop.cmd" and "_uninstall.cmd" (note: include the underscore).
  • A configuration file USBDLM.ini needs to be created. One way is to create an empty file USBDLM.ini and copy it into C:\programs\usbdlm_64\ .
  • Open a "Command Prompt" window and navigate to the USBDLM directory which in this example is C:\programs\usbdlm_64\
  • Run the "_edit-ini.cmd" script which will open the default text editor with administrator rights and load the USBDLM.ini .
  • Copy the lines from the script listing (link) below into the editor. If required, adjust to system specifics, and save the file.
  • The USBDLM.ini configuration file will later instruct USBDLM to set some basic params (optional) and look for a so called ID-file on the USB drive. If this ID-file is found the appropriate configured drive letter will be assigned. Crucial is the section "[DriveLetters10]" of the configuration file.
  • USBDLM.ini (View sample USBDLM.ini configuration file - Copy and paste to use in your own file)

Configuration (on the USB drive)

  • As to the above configuration example USBDLM will be instructed to simply check for an ID-file in the root directory of the USB drive once the drive is being connected. If a matching ID-file is found it will assign the preconfigured drive letter to that drive. In this example the ID-file is called "". This ID-file has only to exist and can be empty.
  • Create a file with the filename "" and place it into the root of the USB drive. A text editor may be used to do so. While the content of the file is irrelevant (it can be empty) I normally add an explanatory line or two to as a hint on the purpose of the file.
  • At this stage the USB drive may still be running and may still have a different drive letter assigned to it. So safely disconnect it by using the Windows "Safely Remove Hardware" function. Then disconnect it or switch it off.

Start and install USBDLM to run as a service

  • Open a "Command Prompt" window (if it was closed) and navigate to the USBDLM directory which in this example is C:\programs\usbdlm_64\
  • Administrator privileges are required to install USBDLM to run as a service. As described before it is recommended to use the scripts provided aiding the installation or removal as well as the stopping and starting of the USBDLM service if required.
  • Use the "_install.cmd" script to install USBDLM to run permanently as Windows service.
  • The USBDLM service is now active!
  • The service will later also start automatically on Windows startup.
  • Changes to the configuration file may be made at any time without stopping and starting the service. Use the "_edit-ini.cmd" script to do so.

Connect USB drive

  • The USB drive can now be connected to the computer.
  • After a few seconds (be patient) the USB drive should register with the preconfigured drive letter. Visibly this will be indicated through the preconfigured (personalized) Balloon Tip e.g. as to the [BalloonTips] section in the configuration file.

Scenario 2:

More than one external USB drive is to be used on a ROTATIONAL basis.

Backup drives will be ROTATED and when connected will always receive the SAME drive letter (as the other one). However, this will NOT work if backup drives will be connected at the same time.



  • If several USB drives are to be used and swapped around on a rotational basis (not connected at the same time) it may be useful to have the same drive letter assigned to each of them.
  • Hard disks can be rotated for safety and security reasons. The same backups (backup sections in TMS Stein's Backup (Pro)) can be performed regardless which of the drive is currently connected. Windows would normally always reassign a different drive letter.


  • The configuration is exactly the same as described under Scenario 1. In addition copy the ID-file "" to the root of all the USB drives which shall be used on a rotational basis (not connected at the same time) and which are supposed to register with the same pre-configured drive letter "Y".

Scenario 3:

  1. More than one external USB drive is to be used on a rotational basis as a backup drive using the same drive letter (same as Scenario 2).
  2. Additional USB drive(s) are to be used either fixed or on a rotational basis.


Configuration (a)

  • The configuration is exactly the same as described under Scenario 1 and 2.

Configuration (b)

  • Assuming another USB drive shall be connected always receiving the same drive letter "Z".
  • Copy the following section (link below) to the end of the USBDLM.ini configuration file.
  • Click to view USBDLM.ini sample file (addition for extra HD)
  • Create the ID-file "" as described under "Configuration (on the USB drive)". Copy the ID-file to the root of the USB drive.

Comments, corrections and additions

Comments, corrections and addition are welcome, contact:

Contact TMS Backup (Pro)