Mistakenly assigned Mac Time Machine, how to restore particialy deleted files to External Scan Disk

Legacy SanDisk Products Ultra II Internal SSD
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Mistakenly used Mac IOS Time Machine to Scan Disk External hard drive, how to recover particialy deleted files

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Hi @SteveSherman
Have you opened a Support Case? If not opened, for more information, please contact the SD Technical Support team for best assistance and troubleshooting:
https://kb.sandisk.com/app/ask

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If you mistakenly assigned your Sandisk external hard drive as a Mac Time Machine backup destination and it started replacing files, you need to stop the process immediately by unplugging the drive or turning off Time Machine in System Settings. I am not sure how much old data on the Sandisk external hard drive has got lost, but, you may try the following methods:

1). Manually Recovering the Files

  • Connect the Sandisk hard drive to your Mac.

  • Open the Sandisk hard in Finder and look for a folder named Backups.backupdb.

    Go to Backups.backupdb > [Your Mac Name].

  • Look for the folder with the most recent date before you mistakenly used the hard drive as Time Machine backup destination.

  • Locate your files within that directory, right-click, and copy them to a different, safe location on your Mac (not the Sandisk external drive).

2). Use data recovery software to get back the lost files

  • Do not add any new files to the Sandisk external hard drive.
  • Download professional hard drive recovery on your internal Mac drive, open the software and select the Sandisk drive to scan for lost data.
  • Look for the original file structure or file types (e.g., .jpg, .mp4) that were deleted.
  • Recover the files to your Mac’s internal hard drive, not the Sandisk drive, to prevent further overwriting. ( Related: Accidentally Erased a Hard drive on Mac? It’s Recoverable )
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if Disk Utility doesn’t show the old volume anymore, you’re past what Finder or Time Machine itself can undo, and the only realistic option is a read-only recovery scan that understands how macOS lays data out on APFS and HFS+. This is where something like Stellar Data Recovery for Mac actually makes sense, not as a magic fix, but because it can scan the raw container without mounting it or triggering more TRIM writes, and it’s decent at reconstructing file metadata if any of it still exists.

The important part is to run it from your internal disk, scan the SanDisk once, and recover only to another drive. If it finds structured folders, great; if it only finds file types, that tells you the filesystem metadata is already gone. Either way, don’t keep experimenting on the same disk. Every extra mount or write just lowers the ceiling on what can be recovered

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I ran into something similar a while ago. First, don’t use the external drive too much right now - any new data could overwrite the deleted files.

If Time Machine was assigned to that external disk, check whether it actually created backups there. Open Time Machine, enter the timeline, and see if you can browse the external disk’s past snapshots. You can restore specific folders or files instead of everything.

If the files were deleted outside of Time Machine or the disk was reformatted, you might need a third-party free Mac data recovery software to scan the external drive. The key is to act quickly and avoid writing new data.