For long-winded reasons I'd rather not explain nor defend, my partner uses Dropbox for a large set of important files (~70G), which are stored on a removable drive. She is also a Windows user. Recently, by introducing a few new drives, I inadvertently changed the drive letter that is assigned to her portable device, which stopped Dropbox from working. Solving this properly is rather finicky so I thought I'd write down what I did.

The end goal is to try and ensure that the portable drive always gets the same drive letter and that Dropbox is configured to use that drive letter, but before I can get that far I need to get Dropbox syncing again. It used to be F:, and I opted for U: going forward.

Luckily the extra letters I'd introduced were all partitions on a separate hard drive from the OS, so I powered the machine down, unplugged the extra hard drive and booted back up. This freed up the stolen drive letters, but the portable drive did not re-inherit them. Running regedit as an administrative user and renaming keys in HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices moved the USB drive back to the correct letter, but I suspected the extra hard drive would take precedence when it was back, so this was only an interim solution.

With the portable drive back on F:, the Dropbox client was happy once again. However I needed to reconfigure the Dropbox client to use a different letter. I wasn't happy with the idea of altering the Dropbox client's configuration database under its feet, so I had to do everything "by the book". Luckily, the client supports the notion of moving your Dropbox folder. Combined with the command-prompt subst command (run as the local user rather than as an admin this time), I was able to clone the F: drive to a virtual U: drive, and then ask Dropbox to move the folder.

subst U: F:\

This was pretty awkward. F:\Dropbox and U:\Dropbox are in fact the same folder, so I needed to ask Dropbox to move it from F: to something other than U:. I opted for U:\tmp. The move took a long time (~2 hours).

The proper solution is to try and get a stable drive letter for her device. This can be achieved using a tool called 'USB Drive letter Manager', or USBDLM. USBDLM is free for educational use, and my partner is a teacher, which is lucky.

Once that's all sorted, reboot, insert portable device, ensure it's on the right drive letter, and move the Dropbox folder back down to U:. This time the move was near instantaneous.


comment 1
Don't drive letter changes made in Disk Management persist, for USB devices? This is how I have a hardcoded high-letter assignment for my Crashplan backup drive
Comment by directhex
comment 2
They probably do, yes. I suspect that "Disk Management" (which I didn't find at the weekend) performs the equivalent of the registry tweaks I made, which are probably persistent after all. The one thing that USBDLM brings to the table is you can configure it so that portable devices that have never been seen are given letters from a range, and push that up past the "jitter" area towards the middle of the alphabet.
comment 3

My partner has an USB drive which she uses for iTunes - so I feel your pain ;-)

We've done the Disk Management jig several times - it is mostly persistent, working for months at a time, but does occasionally lose track for reasons we've never been able to figure out.

(iTunes adds an extra wrinkle where if the drive isn't found in the right place it happily removes the entire contents of your iDevice without warning ... but don't get me started on that rant!)

Comment by David Claughton