I have a 1 TB USB drive.
I've been using it for months.
My main iTunes library is on it.
As of yesterday, for no apparent reason, it has become read only.
I can't open iTunes.
I also tried this...
Here is the info panel on the drive:
Note that the format is currently "Mac OS Extended Case-sensitive."
"Ignore ownership of this volume" is checked, but greyed-out.
Backing it up and reformatting is not practical due to the sheer amount of data.