I was copying a huge file from a USB external drive when it suddenly disappeared from the Finder. I disconnected and connected it back, but the primary partition wouldn't mount. Rebooting the Mac didn't help.

If in the terminal I type
```
diskutil list
```
the primary partition disk4s2 does show up.

It does not show up, however, when I type in
```
df
```
because the partition is indeed not mounted.

I'm now trying
```
sudo fsck_hfs -fy /dev/disk4s2
```
in and the result is 
```
** /dev/rdisk4s2 (NO WRITE)
Can't open /dev/rdisk4s2: Resource busy
```
I've already tried
```
diskutil unmountDisk force /dev/disk4s2
```
and fsck still won't run.

Full disk access is granted to the terminal in security system preferences.

I'm running macOS Ventura on an M1 Max and the drive is an USB external 8TB "WD My Book 25EE Media" formatted to Mac OS Extended (Journaled) i.e. HSF+.

Any ideas on how to make it mount?