On Thu, 5 Dec 2019 at 14:36, home user <mattisonw@comcast.net> wrote:
(Fedora-30)
After doing my weekly incremental back-up, I noticed too much of a drop
in unused space on my USB thumbdrive was unusually low. When I look
inside the end that goes into the port, it's black, which I believe
means it's a USB-2 stick.  It's 16GB.

I tried "Disk Usage Analyzer".  Nice graphs, but no indication of
problems.  This is true both when run as root and when run as a common user.

I tried "Gnome Disks".
1. When I click the part of the graph marked "Filesystem Partition 1 16
GB FAT", it shows beneath the display:
Size 16 GB - 9.9 GB free (38.0% full)
Device /dev/sdb1
UUID 3900-1AD5
Partition Type W95 FAT32 (LBA)
Contents FAT (32-bit version) - Mounted at /run/media/[etc]
2. At the bottom of the display, I click the two gears, and select
"Check Filesystem...".  After confirming, after a couple of seconds, I
get a pop-up saying
Filesystem damaged
Filesystem vfat on  needs repairing.
Results are the same when run as a common user as when run as root.

GSmartControl seems to not know what to do with this thumbdrive.

That's it.  Are there any other tools that can tell me more, like how
much space is unusable, or how many blocks(?) are damaged?  If I ask
"Gnome Disks" to try to repair the filesystem, how much risk is there of
losing data?  Is this thumbdrive on its deathbed?

From my experience, the drive has already lost or corrupted your data.
You may be able to recover some of the files, but attempts to "repair"
the filesystem risk destroying more data.  You can try making a "clone"
of the USB drive using dd, etc. onto a new drive and use repair tools
on the copy.

--
George N. White III