I am mystified that someone can respond with "Problem went away after I rebooted" and have that qualify as an excepted answer. Of course, the problem went away after a reboot. It is a problem with a running process (in this case it's Spotlight). What's interesting is that Spotlight doesn't seem to honor it's Privacy Settings, which should be a source of concern for folks and something that Apple should be admonished for. Here are a couple of pointers to working around the problem (a solution is entirely in Apple's court):
Scenario 1 - you want to have the drive indexed, but you also want to eject the drive temporarily:
Stop the indexing process, eject the drive, and restart the indexing process (this is the bug that Apple needs to fix):
a. sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
b. Eject the drive from Finder, or from the command line with diskutil eject whateverDisk
c. sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
Scenario 2 - you don't want the drive indexed, ever, and you want to eject it.
Stop the indexing process, add the external drive to the Privacy Tab of Spotlight's Settings, under System Settings, add a metadata file to the volume, remove the spotlight files, eject the drive, restart the indexing process:
a. sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
b. sudo touch /Volumes/Whatever/.metadata_never_index
c. sudo rm -fr /Volumes/Whatever/.Spotlight-V100
d. eject the drive from Finder, or from the command line with diskutil eject whateverDisk
e. sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
I hope this helps someone a bit better than "reboot"