4TB My Book formatted as NTFS changes to exFAT "spontaneously"

I have several USB external storage drives connected to my PC tower. All are formatted NTFS, and are used as periodic backup. Doing such a backup, the utility could not write to the drive in question. WD Discovery indicated that the drive was Read-Only. Windows Explorer indicated the file system as exFAT. So how does a file system “spontaneously” change from NTFS to exFAT? More importantly, how do I change it back without reformatting it? WD Drive Utilities indicate that the drive has passed its tests.

There is certainly a lot of conflicting information about exFAT on the web. In theory, Windows should be able to read an exFAT formatted drive. (And apparently exFAT is a Microsoft proprietary format so I would believe that.) But everything I’ve read says that a reformat - which will erase all data - is required to change a drive from NTFS to exFAT. So I would say that the drive could not be changed “spontaneously”, and even if that happened, data would be lost.

I would guess that something has corrupted the drive and is making it appear to be exFAT rather than the drive actually being exFAT.

I’ve also read that a drive formatted on a Mac as HFS+ looks to Windows as an (unreadable) exFAT drive. (I don’t understand the relationship between exFAT and HFS+. I doubt Apple licenses exFAT from Microsoft. The two formats probably just have the same flag bits set.) If somebody tried using your drive on a Mac I suppose you might now have an HFS+ drive.

In any case, I suspect it will be difficult to retrieve your data.

Thank you for your reply. In reviewing my activity with that particular drive, I do recall getting a popup asking if I wanted to do a system backup, which I answered with an “OK”. The problem is that it was not a “Windows” backup but either a Lenovo (the brand of computer I’m using) or a Trend-micro (the anitvirus software I’m using), or the WB application. In any case, it did not ask me which USB drive I wanted to use, but went ahead. Looking over the affected drive, I can see that there was a large amount of data written to the drive, with a date/time stamp close to the time I got the popup. So it is my thinking that the backup process caused the problem. The symptom of the problem is that the drive is effectively locked in “read-only” mode (access to data is there, but additions or deletions are not possible).

Since the data was backed up (this is the second of two drives containing the exact same information), I was not worried about data loss, so I went ahead and reformatted the drive back to NTFS, and started copying the data back onto it. My machines are still at USB 2.0 level, so the copying is taking some time. Last time I did this, it took almost 48 hours. It seems that this time will be about the same.

The lesson here for me is to be very careful about doing the “system backups”, and only use those processes which I can control and verify. The next time I will do such a backup, I will take all external drives offline and have only the intended target drive being connected.