Knowledge Base

Citrix systems have a peculiar drive letter assignment. This article gives description of how to deal with this peculiarity.

Introduction

Citrix systems have non-regular letters mapped to physical volumes (e.g. M for system partition). As a result, restore of a Citrix system can be problematic: the system may become unbootable showing different Winlogon errors, ctxgina.dll error or not finding system drive.

This occurs because whenever the volume SIDs or partition layout changes, Windows will re-letter the drives associated with the system.

There are both proactive and reactive solutions for this problem.

Solution

Citrix official solution

Citrix officials suggest to use a special drive remapping tool (Driveremap.exe), which can be found on the Citrix installation CD.

The following example will remap the servers drives starting with the first available drive to M:

driveremap /u /drive:M

Read the respective article from Citrix KB http://support.citrix.com/article/CTX950520

Proactive solution

When creating the image, it is important to back up the whole system (whole hard disk drives, including EISA partitions). This will ensure that the volume SIDs and partition layout is captured exactly as it appears on the source system.

When performing the image restore, it is important to not change the destination drive size or partition layout. This can be achieved by restoring entire disks at a time rather than selecting partitions one at a time as well as restoring the image to the same sized or larger disk than the source system.

(!) "Full Disk" restoration to a smaller disk still involves an automated partition resize.

Reactive solution

If the proactive solution was not used and the system is unbootable after the restore, it can still be repaired. All that needs to be done is to manually change drive letters back to the original ones (e.g. M for system partition, N, O for other partitions etc).

Manually changing the drive letters requires offline editing of the system registry. There are several options available for editing the registry. Regardless of the method used, access to the restored HKEY_LOCAL_MACHINE hive is required.

Some of the more common methods in editing the hive are done via a PE environment such as BartPE or WinPE, programs such as Far with the registry editor plug-in, RegEdit32 from within another Windows environment accessing the registry remotely, or any other application that can edit an offline and/or remote registry hive.

Once you have access to the restored HKEY_LOCAL_MACHINE hive, do the following:

1. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices. This is where Windows assigns drive letters to volume SIDs.
   

    

   

    

2. To change the drive letters manually, open the REG_BINARY value corresponding to the drive letter that needs to be changed (e.g. \DosDevices\C:)
   

    

    

3. Copy the data.
   

    

   

    

4. Right-click in the white space in the right hand pane and select New -> Binary Value. Name the value with the corresponding drive letter that you would like to change the existing one to (e.g. \DosDevices\M:). Paste the copied data from the existing value to this one.
   

    

   

    

5. Finally, delete the original value keeping the new, correct value.
   

    

    

6. Repeat steps 1 through 5 for all drive letters that need to be changed.
   

    

   

When all of the drive letters have been manually changed reboot the server and everything should come back fine.

More information

To avoid this issue you can also use the Cloning feature of Acronis True Image to transfer the system.

For information how to adjust the Citrix data store settings after duplicating a server see http://support.citrix.com/article/ctx107406