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  • Installing replacement external USB hard drive

    Posted on larryc43230 Comment on the AskWoody Lounge

    Home Forums AskWoody support PC hardware Installing replacement external USB hard drive


    This topic contains 15 replies, has 6 voices, and was last updated by  GoneToPlaid 5 months ago.

    • Author
    • #1908833 Reply

      AskWoody Plus

      My PC (Windows 10 Home Version 1903) has two USB-attached external hard drives (each 2TB) that I use for backing up and archiving files, as follows:

      I:\ External1
      J:\ External2

      Both of the drives are at least three years old, though neither has exhibited any problems.

      Various programs, as well as Windows’ File History feature, use External1 (I:\) to back up all sorts of data.

      I plan to replace External1 with a new, larger drive soon. I’d like to make that process as smooth as possible.

      Do Windows programs (and things like File History) use the drive letter (in this case I:\) or the drive name (in this case External1) to determine what drive to use?

      Can I simply copy all files from the current I:\ drive to a new drive with the same drive letter and/or drive name and expect programs that now point to this drive to begin using the new hard drive?


      • This topic was modified 5 months ago by  larryc43230.
    • #1908839 Reply

      Da Boss

      You can name the new drive through File Explorer.
      You can assign the Drive letter to the new drive through Computer Management\Drive Management.

      You should do the data transfer before you do the name and drive letter changes because you can’t have two with the same label attached at the same time.
      Your programs will probably work OK as long as the destination path is the same, but you should check Settings to be sure File History is pointing at the right place.

    • #1908842 Reply

      Rick Corbett

      I can’t add anything to @pkcano‘s reply except to suggest that for permanently attached USB devices you work backwards for drive lettering, thus reducing any possible conflicts with USB devices that are only attached temporarily and which are using Window’s automatic drive lettering.

      For example, I also have 2 permanently attached external USB hard drive which I’ve manually assigned Z: and Y: as drive letters (well away from any mapped drives) leaving F: onwards free for any temporary attached devices.

      As for whether the OS uses drive letters or drive name, there’s no hard and fast rule (AFAIK)… some backup programs use neither (because they can change) and use the device’s serial no. instead.

      Hope this helps…

      1 user thanked author for this post.
      • #1909352 Reply

        Da Boss

        As @larryc43230 is using the external drives for backup and archiving, it wouldn’t be a good idea to have his permanently conntected like you have yours 🙂

        Remember, don’t leave you backup drive plugged in, otherwise it is a second attached drive waiting for a power surge or virus, not a backup drive.

      • #1910222 Reply

        AskWoody Plus

        I too perform reverse drive letter assignments for my external hard drives. I have a label maker which I used to label the external hard drives not only with the drive’s name, but also with the assigned drive letter. This allows me to make sure that I unplug the correct drive letter after using the safe removal tool in the system tray.

    • #1908902 Reply


      There usually has been a ‘rule’ that Windows would start lettering NAS/Network Attached Storage drives starting with Z: and working back up the alphabet, mine [2] did and all computers seen them as Y: and Z: when mapping the Public Folder on each. The 2 drives are wire-connected to the Router.

      Before you wonder "Am I doing things right," ask "Am I doing the right things?"
      • This reply was modified 5 months ago by  Berton.
      • #1908950 Reply

        Rick Corbett

        Is that automatic, i.e. OS-determined like automatic driver lettering of local storage? I don’t have any NAS devices per se so haven’t come across this yet.

    • #1909615 Reply

      AskWoody Plus

      Thanks, everybody, for your responses. It sounds as if, barring unforeseen glitches, the migration to a larger drive shouldn’t require rocket science.

      For those concerned about connected back-up drives, I also use a third external hard drive as a back up that’s connected only long enough to back up my files. I do this back-up about once a week. In addition, I use Backblaze, which backs up my files continuously in the background. The drive in question (the one I intend to replace) is used mostly to offload files from my C:\ drive.


      • #1910245 Reply

        AskWoody Plus

        Yep, no rocket science involved. After you assign the preferred drive letter to the new drive, the old drive’s fixed drive letter will automatically be removed in the Windows registry when you subsequently plug in the old drive.

        Do you have System Restore points on your old external hard drive? Do you want to preserve them on the new hard drive? If so, then you should use the free version of Macrium Reflect to clone the old external hard drive to the new external hard drive. After cloning the old hard drive and removing it, assign your preferred drive letter to the new external hard drive. Then go to Disk Management and expand the new drive’s partition size to use all of the new drive’s available space, minus approximately 1 GB.

        Why do I not use the final 1 GB? Total available drive space can vary slightly for same-capacity drives from different drive manufacturers, and can vary slightly even for revised drive models from the same manufacturer. Not using the final 1 GB assures that the partition on a drive can be exactly cloned to another same sized hard drive, even if the new hard drive was made by a different manufacturer.

        • #1910348 Reply

          Rick Corbett

          After you assign the preferred drive letter to the new drive, the old drive’s fixed drive letter will automatically be removed in the Windows registry when you subsequently plug in the old drive.

          Umm, sorry but… no it won’t.

          The OP shouldn’t have any problems whatsoever but Windows’ enumeration of USB-attached mass storage devices only ever *adds* a new registry entry based on the device’s vendor/product ID (i.e. HardwareID) and ClassGUID. It does *not* ever remove any previous entry from the enumeration list stored in:


          If you move the device from one USB port to another then the device’s HardwareID and ClassGuid are recorded at:


          Whilst drive letter assignment to devices is fairly dynamic, recording of enumerated USB-attached devices is static.

          This is why apps like Nir Sofer’s USBDeview are so useful in clearing out the accumulated history crud and avoiding the rarely-mentioned USB-enumeration bug that’s been present since Win XP.

          2 users thanked author for this post.
          • #1910373 Reply

            Rick Corbett

            However, the *pointer* to the device will be amended dynamically (*added* with a timestamp, not removed or replaced) in the registry:


            This pointer includes the current drive letter, shown most clearly at:


            Meant to add this to previous post but… AskWoody editing limits. 🙁

            Note: If Windows worked differently, forensic examination could not prove beyond all reasonable doubt that a particular USB mass storage device had ever been attached to a device at a particular time, even if not a file or folder had been opened (in which case this activitity is also stored in the registry… just Google ‘ShellBags’ and ‘ShellBagsMRU’).

            1 user thanked author for this post.
          • #1910599 Reply

            AskWoody Plus

            The drive letter remains in the registry, yet this drive letter gets assigned to the newer drive to which you assigned the fixed drive letter. The info for the older drive which was previously assigned this drive letter is overwritten to point to the newer drive.

            • #1910645 Reply

              Rick Corbett

              The drive letter remains in the registry

              Yes, the last assigned drive letter may remain recorded in the registry (in the expanding DosDevices list)… but will point at the last known endpoint, which may have changed depending upon whether it’s the OS or other (backup) software that is doing the enumeration and recording to the registry.

              Think of USB sticks plugged in and out, all grabbing the next available drive letter. They’ll enumerate and write their HardwareID/ClassGuids to the registry then be assigned a drive letter. Pull them out and re-insert them in different ports. Windows will (try to) assign the same incremental driver letter time after time. Keep doing it though and the USB bug will invariably kick in… and at some point the insertion of the same USB stick will NOT be enumerated in any port. You’ll get an error.

              The drive letter is just an arbitrary OS construct and prone to errors, hence why some backup software uses hardware serial nos instead of drive letters or volume names. Its presence in the registry is not really relevant… it’s what its pointer decribes that is important. It’s just a device IO pointer which is created by the OS when required then recorded in the registry first as a hardware enumeration (what is it?) then immediately afterwards as a direction (how to get to it?) then finally as a direct (but temporary) route (recorded in DosDevices).

              It’s just apparently microscopically faster for Windows to address the device by an arbitrary drive letter than by a computed address (HardwareID/ClassGuid), particularly when so many cheap USB devices don’t have unique serial nos.

              If you want to  check, look at the registry query/write timings for the order in which they occur using something like Sysinternals’ Process Monitor.

              2 users thanked author for this post.
            • #1910718 Reply

              AskWoody Plus

              Very good info. While I do assign drive letters to some of my removable USB hard drives, I do not for other removable USB hard drives which get used for random things. Nor do I assign drive letters to any removable USB memory sticks. I wasn’t aware of this USB enumeration bug. Maybe I have avoided it all of these years by using the above methods? Anyway, thanks again for your detailed information.

            • #1910749 Reply

              Rick Corbett

              I wasn’t aware of this USB enumeration bug.

              It’s not talked about much but is fairly easy to reproduce.

              Take a USB device and plug it into USB port after port. Watch the results. (Nir Sofer’s USBDeview is my favourite.)

              For a while the device will be enumerated accurately, then all of a sudden… NADA, the device will just not enumerate. Seen it happen for years…

              I have no idea whether this is a buffer limit within a particular sub-section of the Windows registry, just that it’s reproducible.

              Check it, please, and report back… so I can verify my own research.

            • #1910890 Reply

              AskWoody Plus

              I have never had this occur, since years ago I learned that Windows (in particular for USB3) does not pay attention to whenever any third party programs are using a USB device. Like I said, generally in particular to USB3 on my Win7 computers. My solution was to disable all power management for all USB hubs (built-in or external) on my Win7 computers. Doing so eliminated all USB dropouts while using 3rd party utilities to either backup or to clone data to external USB drives.

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