Are you aware this has been a problem since the 1998 release of USB?
And it not only impacts USB, but Firewire as well? I hope Thunderbolt is better, but my point is, as long as we rely on asynchronous serial connections, unpredictable power drops will always confuse drives. External drives are best for backup purposes only. I would never depend on them being my primary data source.
SCSI was better, to some extent, but improper termination can cause many issues too.
Hard drives not permanent storage systems. Better than floppy, but still prone to error.
Make at least two copies of your essential data available. Never depend on one source being able to last forever.
With several hundred different external drive manufacturers, it probably is better to go with a few simple known reliable ones such as Newertech, MacAlly GTech, Wiebetech, and LaCie, and pay attention to whether they have firmware updates to fix known issues for the Mac. Otherwise ask, what is their Mac support like. Mac OS X 10.3 had a really bad firmware problem that has periodically reared its ugly head on newer operating systems. Leave a drive connected through a system update, it becomes invisible!
Spotlight losing track of external drives is also a problem because it can also affect visibility. I find it better to depend on Find Any File for file locating.
https://discussions.apple.com/docs/DOC-1689
May help with your external drive data recovery.
Good luck!
