External HD doesn't mount when USB plugged in (Lion) I have an external USB hard drive I use for backing up my MacBook (running the latest Lion).  FWIW, it's a Western Digital internal 3.5" SATA drive in an Antec HD enclosure.  Anyway, of course every so often I have to unplug it so that I can take my MacBook places, so I eject the drive as usual and everything's cool.

But when I plug the drive back in, it doesn't mount.  If I plug it in and then power-cycle the drive itself, then it mounts just fine, but due to how my office is laid out, this is inconvenient.  And, too, I shouldn't have to power-cycle the drive, right?  I should be able just to plug it in and have the MacBook recognize it, no?

So: what's going on and how can I fix it?

Thanks in advance for any and all help.
There is a workaround, sometimes the drive will detect but not mount. If you open Disk Utility it should be listed on the sidebar and you can manually mount it from there.

This doesn't resolve the underlying issue of why OS X hasn't automounted, but if you check in the system logs when you plug it in you might get a clue towards that.