USB Drive changing letter sometimes?

I have 7 USB thumb drives that are all set as f drives. I rotate them around for backing up. They are a mix of USB 2 and USB 3.0. Have used them with this batch file I created for years and no issues. I only use them every couple of months and they are rotated backups.

All of a sudden on desktop my F drive USB 3.0 would say E: was mounted when I plugged it in. I would go to disk management and change it to F. Eject it and plug it back in and most of the time it will go back to E, but not always. Sometimes it stays F. N

Decided to pull out Laptop and see what happens. It does the same and I use different USB thumb drives so it is not a thumb drive issue. Right now I have a thumb drive in laptop and it stays F as I assigned it and it should be, plug it into desktop and it goes to E same USB drive. Take it back to laptop and E. Disk management doesn't show any F drive when it goes to E. I can go into disk management and change it back to F. If I don't change it and just plug it back into laptop, it will usually be F as it should be, but not always.

Just now pulled it out of laptop where it was assigned F and plugged into desktop and it actually stayed F. You just never know?? Prior to last switch to desktop I did a diskpart command of list volume. I notice it had a volume 3 with no letter, no label, no data, type removable, status no media. I also see Volume 0 (D) type CD,1 (no letter Recovery) type partition,2(C: OS) type partition and I know what they are as they came with system. After I plug in the USB there is a volume 4 which shows as it should F, NTSF, type removable, 239GB, healthy.

However it is doesn't always change to E. I wish I could find a constant of what is happening, but not finding that. Laptop is on Windows 10 22H2 19045.3448 and desktop on 19045.3570.

Assuming that you are assigning a drive letter to a USB drive, note that only a single physical drive can be reliably assigned to a given drive letter.

Further, very occasionally it's been seen that the assigned drive letter is completely lost, even if only 1 physical drive has been assigned that letter.

You might consider making use of the hardware id of the drive as an alternative in some circumstances. I seem to remember hearing that Macrium Reflect, for example, supports that.

If you are using batch files then make two of them. One using E: and one using F: as destinations. After you determine which one is assigned then use the appropriate batch file.

I'm actually surprised that you've had it working as consistently as you described.

I did once try a quick experiment with assigning the same drive letter to two different flash drives, and after swapping them, found only the most recently inserted one retained the drive letter I'd assigned both.

Like you, for Macrium R, I use a backup drive with a letter later in the alphabet assigned for consistency.

For interest - here's the MR option for using the Volume GUID rather than the backup drive letter:

diverjer said:

Even will change when I move the thumb drive to my laptop

The drive letter assignments you make on one computer do not affect other computers. They are Windows settings not device settings.

Alternatively, the use of device labels in scripts is permanent because drive labels are a device setting. But this approach can only be used in scripts and has no effect on, for example, any backup utilities you have installed.
A script can be written to take a drive label you pass to it and return the drive letter for the drive with that label.
e.g.
Pass the drive label Fred and get back the drive letter J:\ that it is currently using.
I can post an example if you are going to use this approach in scripts.


Denis

diverjer said:

Sometimes it is J other times not, goes to E.

Yes, as you've reported, Windows can lose the drive letter assignment.

diverjer said:

That doesn't seem to be the case for me, seems I can get different drive letters assigned on same computer.

Yes, but not at the same time surely. Your desired drive letter assignment is either lost or not lost.

Drive letter assignments are saved in the Registry at the bottom of this Key
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
So you could run a script to see if one had been lost.
If you want to restore a particular drive letter assignment that has been lost it should be possible.
See Transferring drive letter assignments - my post #32 -ElevenForum

Attempts to use that Key to restore all drive letter assignments have been found to be awkward.
You'll be able to see the awkwardness by reading the posts following that one. I stopped working on it because it was more effort than just setting them up again manually.


Best of luck,
Denis

FWIW - my experience of 3 drives to which I have assigned letters late in the alphabet (so the letter isn't used by anything else) - 2 used on 1 laptop, 1 on another as backup drives. The two I use on 1 laptop are assigned different letters.

These are usually consistently stable. Only very occasionally have I found the letter assignment is lost.

There may be a different approach- using the hardware id of the drives. I believe I've read Macrium Reflect can do that.

I did once experiment by having two drives assigned the same letter. Using the second meant the first lost its assignment.

I'm wondering - since you used F: - if you already have a drive E: - so F: is simply the next available in the alphabet. That may be why you could use a number of drives - until perhaps you did that with another drive already in place using F: - in which case F: wouldn't be available.

I suggest you try the 2 drive experiment with, say drive letter R: (late in the alphabet).