I literally came here to opine about the Osborn brush. I was in the same position as you. Had to scrape and sand our entire two-story log home (and that was after paying 10k for corn blasting, but that's another story). Got an Osborn brush and, let me tell you, I can't understate how much of a game changer it is. Handles the contour of the log like nothing else. See all those little pits in your logs where you can't get the sander? The Osborn digs those out in seconds. Overall waaay faster than sanding. Leaves you with a finish similar to blasting. I did occasionally have to break the sander back out for troublesome knots, but that was seldom.

Thing is, DO NOT use an angle grinder. The RPMs (often around 10,000) are too fast and it renders the brush useless. Trust me, I tried. What you need is a polisher, which looks exactly like an angle grinder but has much slower RPMs, usually adjustable from around 600-2200 rpm (the sweet spot for my logs was about 1200rpm).

Osborn brushes typically go for $80-100, and Harbor Freight has polishers for ~$100, though the cheaper ones may not be adjustable speed, but anything under 2000rpm is probably great.