Windows XP will assign a drive letter already in use for mapped network drives to any external USB Storage Device

Posted on 2008-11-19
Last Modified: 2013-11-14
I noticed that every time I plug an external USB storage device Windows will not recognize it because it give it a drive letter that is already in use for one of my mapped network drives. To get the USB storage device to work I need to go to the Disk Management utility and I have to change the drive letter to something else in order to be able to access my drive. This happened on more than one occasion, and recently it happens every time I connect a USB storage device?

What is causing this and is there a fix? :)
Question by:CUOL-MIS
    LVL 59

    Assisted Solution

    Not sure what causes it (will research that shortly), but I think this Previously Answered Question might have your answer for how to fix it (use the capability to mount drives):
    Setting default drive letter to be assigned to USB storage device
    LVL 24

    Accepted Solution

    This is a 'feature' of XP. It will assign a hard drive the next letter it can without considering mapped drives. To solve this issue all my mapped drives are assigned from the end of the alphabet and my physical drives are assigned from the beginning.
    I hope this helps. Good luck.

    Author Comment

    I think I found the answer, and you are both correct....

    "Drive Letter Conflict with Network or Subst Drives

    Since XP Network and Subst drives are no more global, they exist in the context of the user who created them only. In the context 'System' where the Mount Manager assigns drive letters such drives are not visible offhand. Therefore they are not considered by XP. If there is a network drive on the first available local letter then XP assigns it again to a new external drive. The external drive is invisible and unaccessible then until its drive letter is changed in the Disk Management (right click My Computer -> Manage -> Disk management) or by my commandline tool ReMount. But for each new drive you have to change the drive letter again and it's no solution to assign a letter again to a different external drive because XP can save exactly one assignment per letter.
    So change the network drive's letter to a higher one to get the lower ones available for external drives. Or let my USB drive letter manager change the letters of USB drives for you.
    Microsoft is aware of this and calls it a problem. Meanwhile a hotfix is available (WindowsXP-KB297694-x86-ENU.exe) and the XP Service Pack 3 fixes the problem too.
    What the SP3 did not fix is this scenario: Letters C: + D: used for local drives, E: for an USB drive. Remove the USB drive, create a network drive at E: and reattach the the USB drive again. XP with SP3 will assign E: anyway, the USB drive is 'hidden'. This is fixed in Vista.
    The problem persists when an external drive is attached before the user logs on. The mapping of the network drives fails when their drive letter is in use. USBDLM fixes this when configured appropriate. "


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