I happened to sign on to my desktop Mac and noticed something very strange, the Harddisk icon was no longer on the desktop.
Other clever tricks for looking at the file systems showed the file was most certainly present, although Finder operations were treating the volume as if the hard disk was hidden or invisible. The drive was there when I used terminal and did $ ls -l /Volumes
Finder Preferences showed that icons should be shown, but just the drive icon wasn’t appearing.
Then I found this aritcle, which suggested firing up the Script Editor and running this script:
tell application “System Events”
set visible of disk “NameofDisk” to true
end tell
tell application “Finder” to quit
delay 1
tell application “Finder” to launch
I believe I got myself into trouble by accident when I did the last disk repair using Disk Warrior or Disk Utility. Somehow the operation marked the drive as invisible. Undoing it was as simple as asking the system to make it visible again.