This drive is being used only for the backups I mentioned. Anyway, the point is that there is ample contiguous free space both before and after these backups. I would expect NO fragmentation at all. But I get a lot of it.
My understanding is that the following algorythm is fundamental to most file systems, including NTFS:
START given an object (a file or fragment) to be stored,
IF one or more available contiguous spaces are sufficient to store the entire object, use the smallest one of them and you're DONE.
ELSE use the largest available contiguous space. Use all of it, storing as much of the object as will fit in the space.
This leaves a fragment still to be stored. GO TO START.
So, why do I get fragments?
Maybe because of the Acronis software, or because it's coming in over-the-LAN, or both?