Copy Verification

[RDFrelay]

This may be a basic question, but here goes...

When I burn a DVD, Toast will "verify" the copy after the burn is complete.

When the Mac copies a file, does this verification happen automatically?

Another way of asking this is-- can I be certain that the file was copied accurately, or is there a possiblity that the copy is corrupted?

[dnanian]

Toast has to verify because CD-ROMs often burn "wrong". Hard drives, on the other hand, have controllers that verify writes. So there's little reason to verify again, because you'll get an error if the wrong was wrong.

(Think about it like saving a file to your drive - Pages doesn't re-check the save, because you get an error if it fails.)

[RDFrelay]

Thanks again, Dave. I see, the hard drive controller does the verification step as it writes.

Is it possible for the hard drive controller to believe that the file was copied accurately (i.e., not report an error), but for the copy of the file to nevertheless be corrupted?

I'm trying to determine how paranoid I should be that a file that is backed up didn't get copied correctly. Another way of asking this is, if a copy a file to an external drive, how safe is it to delete the original without checking the copy?

[dnanian]

It's always possible for things to corrupt... after all, that's why you need the backup in the first place. But the likelihood is extremely low that it would become damaged immediately upon copy without error.

Critical data, though... remember that redundancy is your friend.