Can't rename any drive to "M"

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  1. Posts : 15
    Windows 10 Home (x64) Build 18363.815
       #1

    Can't rename any drive to "M"


    When I try to rename any drive, external or internal, the drive isn't seen in "This PC". Any other letter works fine. The renamed drive can be seen and even accessed (right click > open) in Disk Management or MiniTool. It was suggested that I try "mountvol /r" but to no avail. Of course the easy fix is to just pick another designation. But that would keep me up at night.

    Any ideas?

    Thanks
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  2. Brink's Avatar
    Posts : 48,772
    64-bit Windows 10 Pro for Workstations build 19635
       #2

    Hello Jaycee,

    Do you mean you can't change the drive letter to "M" instead of the name?

    If so, check using Option 4 in the tutorial below to see if "M" has already been assigned to another drive. If it has and you don't want that drive to have "M" anymore, then delete the \DosDevices\M: value to have it available.

    Change and Assign Drive Letter in Windows 10
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  3. Posts : 15
    Windows 10 Home (x64) Build 18363.815
    Thread Starter
       #3

    When I go into Disk Management and right click "Change Drive Letter and Paths" a screen opens with the options ADD CHANGE and REMOVE. I click CHANGE and a screen open with a list of available drive letters. If I choose M the drive disappears from Explorer/This PC. But it can still be seen and opened with Disk Management. \DosDevice\M: appears in the registry. If I repeat the procedure and choose any other available letter (other than M) the drive again appears in My PC. \DosDevice\M: is no longer in the registry but the new letter does.
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  4. Brink's Avatar
    Posts : 48,772
    64-bit Windows 10 Pro for Workstations build 19635
       #4

    Hmm, I'm not sure why it does this only with the "M" drive letter.
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  5. Posts : 15
    Windows 10 Home (x64) Build 18363.815
    Thread Starter
       #5

    Nobody seems to have any idea why only "M" can't be assigned.
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  6. CountMike's Avatar
    Posts : 16,647
    W10 Insider + Linux
       #6

    JayceeM said:
    Nobody seems to have any idea why only "M" can't be assigned.
    It might be reserved for some other drive connected in the past.
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  7. Kari's Avatar
    Posts : 17,113
    Windows 10 Pro
       #7

    JayceeM said:
    Nobody seems to have any idea why only "M" can't be assigned.
    Open an elevated Command Prompt. Run Windows Disk Partition Tool with following command:

    diskpart

    Check all currently used volume letters:

    list vol

    Close DISKPART:

    exit

    Can't rename any drive to "M"-image.png

    Check if the M is used, and if yes, which volume is using it.

    Kari
      My Computer


  8. Posts : 15
    Windows 10 Home (x64) Build 18363.815
    Thread Starter
       #8

    Kari said:
    Check if the M is used, and if yes, which volume is using it.

    Kari
    Nothing is listed as an M drive.

    - - - Updated - - -

    CountMike said:
    It might be reserved for some other drive connected in the past.
    How can I tell?

    - - - Updated - - -
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  9. f14tomcat's Avatar
    Posts : 47,375
    Triple boot - Win 10 Pro, Win 10 Pro Insider (2) - (and a sprinkling of VMs)
       #9

    In the same area of the Registry, check for any "offline" devices, possibly Drive Letter M.

    I have some hidden intentionally.

    Can't rename any drive to "M"-2019-04-16_07h39_24.png
      My Computers

  10. Kari's Avatar
    Posts : 17,113
    Windows 10 Pro
       #10

    JayceeM said:
    Nothing is listed as an M drive.
    Could it be that you have mapped a network drive with letter M?

    There's a fundamental flaw in Windows Disk Management, it has always been there and Microsoft seems unwilling to fix it. Disk Management does not flag drive letters used by mapped network drives as used.

    Example from my laptop just now. I have a partition W with label MDT. I also have three mapped network drives X, Y and Z. To get the screenshot, I changed MDT partition's drive letter to X, a letter currently used by one of the mapped network drives. Disk Management accepts the drive letter change, not showing mapped network drive letters X, Y and Z as used, but after the letter change the MDT partition disappears from Explorer.

    In screenshot, #1 is the mapped network drive X, #2 shows that Disk Management has accepted the letter change to X, a letter already used by a mapped network drive, and #3 shows that because of drive letter conflict, my MDT partition is no longer shown in Explorer where it should be:

    Can't rename any drive to "M"-image.png
    (Click to enlarge.)

    As soon as I change the drive letter back to W for my MDT partition, it will reappear in Explorer.

    If you have mapped a network drive with letter M, it would explain your issue.

    Kari
      My Computer


 
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