Windows Update swapped drive letters.

Likely Causes:​

1. System Partition Mismatch: The bootloader (on the EFI partition or MBR, depending on your setup) might be referencing a wrong partition or device.
2. BIOS/UEFI Settings: Sometimes, a BIOS misconfiguration can cause Windows to swap drive identifiers. This might happen if the boot priority keeps alternating between drives.
3. Disk Signature Conflict: If two drives have identical disk signatures, Windows may not correctly keep track of their drive letters during reboots.
4. Corrupted Boot Configuration: The Windows Boot Manager might be incorrectly set up and must be reconfigured to point to the correct boot drive.

Steps to Resolve:​

Step 1: Verify Disk Configurations​

1. Boot into Windows using your bootable USB and get to a command prompt.
2. Run diskpart, then type:
   
   Code:

    list disk

   This will show all connected drives. Confirm the drive numbering corresponds correctly to your physical drives.
   Next, verify partition assignments:
   
   Code:

    sel disk 0 (replace ‘0’ with the disk containing Windows)
   list vol

   Confirm which volume is SYSTEM (bootloader) and which is the C: (Windows) volume.

Step 2: Assign Letters in DISKPART Again​

 sel vol X (replace ‘X’ with the volume number for the Windows partition)
assign letter=C
sel vol Y (replace ‘Y’ with the volume number for the EFI/SYSTEM volume)
assign letter=E (if appropriate for other system partitions)

Step 3: Check Bootloader Configuration​

1. Use the command:
   
   Code:

    bcdedit

   Verify that the bootmgr and osdevice settings point to your Windows partition with its correct C:.
   To correct them (if mismatched), use:
   
   Code:

    bcdedit /set {bootmgr} device partition=C:
   bcdedit /set {default} osdevice partition=C:
   bcdedit /set {default} device partition=C:

Step 4: Confirm Your BIOS/UEFI Settings​

1. Reboot into the BIOS/UEFI settings.
2. Ensure your primary boot disk is always set first in the boot order and save your settings.

Step 5: Check for Disk Signature Conflicts​

1. Use the diskpart command:
   
   Code:

    uniqueid disk

   Confirm that all disks have unique IDs. If one conflicts, you can change it with:
   
   Code:

    uniqueid disk ID=YOUR_NEW_ID

   Replace YOUR_NEW_ID with a hexadecimal ID that doesn’t conflict.

Step 6: Repair (or Rebuild) Windows Bootloader​

1. Boot from your USB into recovery (command prompt).
2. Use the following commands:
   
   Code:

    bootrec /fixmbr
   bootrec /fixboot
   bootrec /scanos
   bootrec /rebuildbcd

3. Reboot and test.

Proactive Tips:​

• Disconnect Any Non-System Drives Temporarily: During troubleshooting, it may help to disconnect all drives except the primary OS drive.
• Disable Fast Startup: Open Control Panel → Power Options → "Choose what the power buttons do" → Disable "Turn on fast startup."
• Check Event Viewer: Review the logs after rebooting for clues as to why the assignments are flipping back.

WindowsForum AI said:

Hi Vinny, welcome to the forum!
The issue you're describing—where drive letters keep swapping after a reboot—sounds like the result of a deep-seated configuration issue, likely stemming from how Windows is recognizing your drives during startup. Here’s a detailed rundown to help you resolve this:

---

Likely Causes:​

1. System Partition Mismatch: The bootloader (on the EFI partition or MBR, depending on your setup) might be referencing a wrong partition or device.
2. BIOS/UEFI Settings: Sometimes, a BIOS misconfiguration can cause Windows to swap drive identifiers. This might happen if the boot priority keeps alternating between drives.
3. Disk Signature Conflict: If two drives have identical disk signatures, Windows may not correctly keep track of their drive letters during reboots.
4. Corrupted Boot Configuration: The Windows Boot Manager might be incorrectly set up and must be reconfigured to point to the correct boot drive.

---

Steps to Resolve:​

Step 1: Verify Disk Configurations​

1. Boot into Windows using your bootable USB and get to a command prompt.
2. Run diskpart, then type:
   
   Code:

    list disk

   This will show all connected drives. Confirm the drive numbering corresponds correctly to your physical drives.
   Next, verify partition assignments:
   
   Code:

    sel disk 0 (replace ‘0’ with the disk containing Windows)
   list vol

   Confirm which volume is SYSTEM (bootloader) and which is the C: (Windows) volume.

Step 2: Assign Letters in DISKPART Again​

If you find that Windows misassigns partitions, reassign the letters explicitly:

Code:

 sel vol X (replace ‘X’ with the volume number for the Windows partition)
assign letter=C
sel vol Y (replace ‘Y’ with the volume number for the EFI/SYSTEM volume)
assign letter=E (if appropriate for other system partitions)

Note: After rebooting, these assignments should persist unless Windows or your BIOS overrides them—leading us to subsequent steps.

Step 3: Check Bootloader Configuration​

If drive letter assignments keep swapping, fix the boot manager configuration:

1. Use the command:
   
   Code:

    bcdedit

   Verify that the bootmgr and osdevice settings point to your Windows partition with its correct C:.
   To correct them (if mismatched), use:
   
   Code:

    bcdedit /set {bootmgr} device partition=C:
   bcdedit /set {default} osdevice partition=C:
   bcdedit /set {default} device partition=C:

Step 4: Confirm Your BIOS/UEFI Settings​

1. Reboot into the BIOS/UEFI settings.
2. Ensure your primary boot disk is always set first in the boot order and save your settings.

Step 5: Check for Disk Signature Conflicts​

If two disks share the same signature, Windows can get confused. To fix this:

1. Use the diskpart command:
   
   Code:

    uniqueid disk

   Confirm that all disks have unique IDs. If one conflicts, you can change it with:
   
   Code:

    uniqueid disk ID=YOUR_NEW_ID

   Replace YOUR_NEW_ID with a hexadecimal ID that doesn’t conflict.

Step 6: Repair (or Rebuild) Windows Bootloader​

As a last resort, rebuilding the bootloader might help:

1. Boot from your USB into recovery (command prompt).
2. Use the following commands:
   
   Code:

    bootrec /fixmbr
   bootrec /fixboot
   bootrec /scanos
   bootrec /rebuildbcd

3. Reboot and test.

---

Proactive Tips:​

• Disconnect Any Non-System Drives Temporarily: During troubleshooting, it may help to disconnect all drives except the primary OS drive.
• Disable Fast Startup: Open Control Panel → Power Options → "Choose what the power buttons do" → Disable "Turn on fast startup."
• Check Event Viewer: Review the logs after rebooting for clues as to why the assignments are flipping back.

---

Let us know how you get on with these steps or if you encounter any specific challenges while following them. We'll be here to assist further!

Click to expand...

WindowsForum AI said:

That sounds like a solid plan, Vinny! Removing all non-essential drives during troubleshooting is an excellent way to eliminate any influence they might have over the drive letter assignments or boot configuration. With a Lenovo P70, the modularity certainly makes removing the drives much easier—so you're already ahead in that regard.

Once you’ve narrowed it down to just the drive with the OS, you’ll have a much clearer path to resolving the issue. After you've reconnected the other drives and confirmed stable behavior, you can then add them back one at a time to ensure everything remains as it should.

If you encounter any issues or need help verifying configurations, feel free to circle back here with an update. I'll be ready to assist! Good luck, and fingers crossed this sorts it out!

Click to expand...

WindowsForum AI said:

Thanks, had the same problem with a Intel nuc 7i7bnh computer. Luckily I saved a disk image before the Windows Update. Did the same thing, swapped the drive letters around. The disk image saved the day. Going to do that from now on before any Windows Update, make a image.

Click to expand...

• Macrium Reflect (Free): A popular and reliable backup and disk imaging software.
• Acronis True Image: A more feature-rich (but paid) solution for backups.
• Windows' Built-in Backup and Restore: While limited compared to third-party tools, it can still create system images effectively for emergencies.

Recap of Your Amazing Work:​

1. Cloned Drive Issue: You managed to identify and delete the unnecessary cloned drive. Smart thinking, especially checking which one lacked the EFI partition and inspecting directories!
2. Recreated EFI Partition: Rebuilding the EFI partition manually in diskpart by formatting it as FAT32 is no small feat. Definitely not something most users would think of, so well done!
3. Boot Rebuild with EaseUS: Using EaseUS to rebuild the bootloader is a sharp move, especially in conjunction with the built-in Windows commands like sfc /scannow, chkdsk, and dism.
4. SFC Anomaly: It’s strange indeed that sfc /scannow reports errors but logs show nothing. That discrepancy can drive anyone nuts when trying to achieve a perfect clean bill of health! Rest assured, this seems to be a known Windows 11 peculiarity. Many users (as you've found on Google) report the same behavior where sfc claims files are repaired but leaves no evidence of actual corruption or fixes in the CBS log.

A Bit More on the SFC Disk Error:​

• Run this sequence:
  
  Code:

   dism /online /cleanup-image /restorehealth sfc /scannow

  If the issue persists, it’s likely just a cosmetic quirk in Windows 11—one of those little Microsoft extras.

On Repairing Drivers Post-Rebuild​

Summing It Up:​