SD! drive won't unmount/eject
 

I have two identical, brand-new 2 TB LaCie external drives I'm using for backups: One for SuperDuper!, one for Time Machine. Almost every time I attempt to unmount or eject the SuperDuper! drive, it fails with the message "Make sure that all applications and files are closed on this disk." If any apps/docs are open, I close them...but still can't unmount/eject the drive. I don't have this problem with the Time Machine drive.

Any ideas?

Spotlight or AntiVirus? Try disabling any AntiVirus and adding the backup drive to the Spotlight Preference Pane's "Privacy" tab.

No AntiVirus, and no (apparent) Spotlight activity. But whatever it is, why would it only affect the SD! drive, and not the TM drive?

We definitely don't have anything open on the drive, Nick. You can use a command-line tool, lsof, to see what's open. The syntax would be

sudo lsof | grep "The-volume-drive-name"

And that would give a list of the files open on that volume. Might give you a hint.