Because @Puqeko showed more interest in my comment. I thought I would provide more information. This is not an answer, I'm afraid, but it will provide a bit more information on the error I experienced, which I think is the same:

"Initial" drive state:

I found a thumb drive in my house. It was fairly old; I checked its contents, and found it empty. However, I also found this on the Mac's "info" (Command-I in Finder) and "Disk Utility":

Mac's Info from Finder:

Disk Utility:

As you'll note in both cases (using either method), there is a capacity of only 129 MB, but an available of 704 MB. Disk Utility will even claim that I am using "-575 MB".

The truth is that it was empty, I used Disc Utility to erase it all, actually.

I re-erased the drive using Disk Utility, this time with the "slow & secure" erase. No difference, it all looked the same. Aside from the screen shots above, I also looked at the drive using df -h.

Via linux, the drive is still showing only 129 MB capacity, but more importantly, it does not have any of the -575 MB used, and it does not show the 704 MB remaining. So things look normal in the command line.

After adding a file:

I then tried to put some files that were larger than 129 MB onto the drive, no luck. So, it seems, the drive really is only 129 MB. I then put a smaller file on the drive (~ 103 MB), and both Finder & Disk Utility looked as expected:

Finder:

Disk Utility:

Summary

I here replicated the problem the OP had, showed that - in my case - the negative space was false, and showed that I could get things to "look normal" simply after changing its state, in this case, by adding a file.

Not much help, but at least it gave a means to reproduce, and another example.

Mike Williamson

Posted 2016-01-31T21:39:41.370

Reputation: 152

1This does seem to replicate the issue. However, I tried coping ~1GB worth of files across after reading the above. It now says -813MB used, 19.52GB available??? The USB drive I have was also supposed to be empty in the question. However, it is relatively new (2 months old). Interesting how Mac's "info" displays -- yet disk utility displays -575.4 (this is also true on my machine). I still cannot find anywhere on the net that can explain this behaviour. Thanks for adding your info. Much appreciated. – puqeko – 2016-02-03T21:44:27.277

You're welcome! We'll see if anyone with further details can chime in with real answers... ;-p – Mike Williamson – 2016-02-04T21:09:18.563

I have seen the same case with a USB drive. It's an old drive that I THINK should have 1 GB of space. It similarly shows the space by providing a low capacity of 0.2 GB, a negative space of -0.8GB, and a total of ~ 1GB. – Mike Williamson – 2016-02-01T22:57:34.793

@MikeWilliamson That is interesting. There is also a similar question here on super user. But the answer simply states it is a hardware problem. I'm more interested in how and why this happens. Thanks for sharing. :)

– puqeko – 2016-02-02T05:08:28.343

How does disk utility show negative disk usage for a USB Drive?

Answers

"Initial" drive state:

After adding a file:

Summary