Thumb drives are not considered a reliable means of long-term storage. As a general statement, they have a high-failure rate.

Traditional hard drives and SSDs are much more reliable.

thumb drives as a transfer medium.

As I said, I was in the process of loading the folders from my Mac to the thumbdrive. The thumb drive was still connected to the Mac when I noticed that some disappeared. I still had plenty of capacity left on the drive.

Then run it on your USB drive. Roadkil Undelete is one that comes to mind. There are others here:
http://www.photo-freeware.net/

If the usb drive has failed (and I suspect it is more a file format problem than a failed drive) try Partition Find and Mount which MAY show you files on the drive to expedite recovery. http://findandmount.com/

If they still exist, they would be on my old Mac.

command on the files instead of just a copy.

Did you use a commercial software to move them over?

But they may have been copied to the usb drive and for whatever reason are not showing up, ie. an error in the file allocation table (FAT). I haven't used a Mac since the 90s but if you trawl the Mac enthusiast sites you may find a free recovery tool to try.

Any software would have to be ancient enough to run on OS 9

Lots of them on eBay. What they do is modify the Flash Drive internal code so that a 8GB looks like a 64GB Drive. I bought more than a few 64GB off ebay that were bad, I was seeing anything over 10GB was rewriting and corrupting files. I found if you can fill 50% of the thumb drive with video files, pull it out and put it back in and play the video then you got a good thumb drive. Flash drive tester showed ????? for 80% of the address locations. By the way, the ebay seller sent me good replacements that works great.

Buy a name brand quality flash drive, I never had a problem with sandisk or pny

I bought it at office depot a long time ago. I can understand that being the problem, but why would my original files disappear?

It worked fine until . . .

I've altered my approach, though it adds time to the process. I first duplicate the file, then drag and drop the duplicate. After seeing that the file transferred properly to the thumb drive, I then delete the duplicate on the Mac.

if the transfer was successful and then delete the originals if necessary. It takes more time as you said but it eliminates problems.
And I make more than one backup of anything I want to keep.
I've got files going back over 20 years saved in more than one medium. I still have data DVDs of my original mp3 files-they're backed up on flash drives, external hard drives and on 3 different computers
I learned my lesson when I lost 4 months worth of recording data.

I still have data on zip drives.

Even on Windows, dragging files from one partition to another copies the files. Files are moved, not copied, when dragging from one folder/directory to another on the same partition.

Last edited Fri Aug 12, 2016, 02:05 AM - Edit history (1)

Mac uses different file system as PC. You should find thumb drive supports FAT 32, such as SanDisk. Instead, you can backup files to mac with this file transfer. It is more convenient than other ways.