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I recently upgraded my D: data drive to a larger one, like so:

  • installed the new drive as E:
  • copied all the files from D:\ to E:\ using robocopy
  • powered off the PC, removed the D: drive permanently

However, I can't change the E: drive back to D: -- that is, when I try to change the letter in Disk Manager the letter D: simply doesn't show up as available.

Why not, and how do I fix this?

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Have you rebooted since removing D:? –  Traveling Tech Guy Oct 16 '11 at 22:56
    
yes, I had to reboot to remove D otherwise it'd be a live drive removal.. I guess that's allowed? I'm not ballsy enough to rip a drive out while the system is running! –  Jeff Atwood Oct 17 '11 at 21:44
    
Nothing to do with ballsy - don't yank out components from a running machine. You may lose data, or worse, short something out –  Traveling Tech Guy Oct 17 '11 at 22:43

1 Answer 1

up vote 7 down vote accepted

For some reason, Windows likes to reserve drive letters it previously saw.

This information is stored in the registry at

HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices

enter image description here

Simply delete the registry key of the unused drive letter at \DosDevices\D: , then restart, and you'll be able to re-use the desired drive letter.

After doing this a second time, I found that it's easier if you do it this way:

  1. Transfer all the files from the old data drive D:\, to the new data drive E:\.

  2. Do not reboot!

  3. Make sure absolutely no programs are running that are accessing files on the old data drive. Shut down as many apps as possible. Then change the drive letter of the old data drive to something random D:\Q:\.

  4. Now you can change the drive letter of the new data drive to the letter that was previously occupied by the old data drive, E:\D:\

Basically, change the drive letters with both old and new data drives connected; don't reboot until you have performed the drive letter switcheroo. That would avoid the problem I had above.

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2  
Next time, assign E to D. Windows will say it won't reassign them until you reboot. When you reboot, it will do its thing. –  surfasb Oct 16 '11 at 23:12
    
@surfas that does not work, because I cannot assign a drive letter to another in use drive letter -- it does not appear in the eligible list of letters. But I updated my answer to clarify how you can do it! –  Jeff Atwood Aug 1 '12 at 0:13

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