Fixing External Drives Ejecting on OS X 10.8

So I’ve been having a problem with external drives continually ejecting over and over again immediately after mounting. After replacing a drive and still having the same damn problem I’ve finally figured out the problem.

Spotlight.

The problems were being caused by Spotlight’s indexing of the external drives. I don’t know why spotlight is causing the issue, but after excluding the external drive from Spotlight’s index, the problem stopped occurring.

You can exclude the drive from Spotlight’s index by going to System Preferences → Spotlight → Privacy and click the + sign at the bottom and add your external drive (assuming it stays connected long enough for you to do so - it can be a timing game).

Then I disconnected the drive for a few days and Spotlight forgot that I told it to not index the drive and restarted ejecting it again. I had to go back into the Spotlight preference pane and exclude the drive again.

Caveat

If you tell Spotlight not to index a Time Machine drive, it will politely tell you to go screw yourself. I ran across this because my external drive is split between an archive drive and my Time Machine backup, so the drive kept ejecting for a while.

In my case, I let it run when I left for work and eventually (I guess) Spotlight finally indexed whatever was causing it to eject and the problem went away. Since doing this, I haven’t had any problems.