Good point, thanks. My knowledge of tape backup software is stone-age, and its probably improved since, but the worry in my mind was the tape backup being asked to copy an "in use" file; my recollection is that what the tape backup did, when it found a file was in-use, was to add it to a list to "try again later" - e.g. at the end of the rest of the backup process. If that's the case then I suppose it is inconceivable that SQL would release the file lock on one of the MDF/LDF files and not the other, or lock one-but-not-the-other at different moments in time, so on that basis whatever is on tape should be fine. Makes me nervous though, but maybe that's totally irrational?