External Hard disk questions

If I run 'verify disk' in disk utilities and t shows nothing wrong - checks 'ok', then is that for the files that are on it, including the OS only, or is it also telling me there is nothing physically wrong with the drive itself?

Disk Utility is limited in what it can test. Files, folders, etc. but the physical and electronic integrity of the drive are not checked. A good SMART utility can do more but no utility is fool proof when it comes to doing a 100% checkout of the drive.

Thank you for the prompt response... The drive in question is my newest external. I've had it for the better part of the year. It fell off the desk 1 time, but seemingly didn't suffer any consequences until I loaded Yosemite on it (upgrade & clean install), and when that didn't work (thinking it's the new OS) I tried putting Snow leopard back on it, used it for backup (of SL) and it just won't do what it's supposed to do. I've used CCC, time machine and Super duper... all fail just before completing the backup. This works both ways - backup from and backup to.
Any other program/app suggestions for testing this?
And before it's asked, I don't have the purchase receipt to do a warranty claim :-(
Thanks in advance for any help!!

I just noticed this is posted at 1 A.M. Where the heck is it 1 A.M. ?!!

It does sound like the drive may have suffered some mechanical damage when it was dropped. There's really no test that can tell you exactly what was damaged. As far as warranty is concerned, I have never needed a receipt when requesting a RMA from the manufacturer. All they generally want to know is the nomenclature off the drive and SN from which they can tell when it was approximately purchased.

Okay... Thank you

Update - Turns out drive needed firmware update. Who knew?!! lol.