advice on speeding up the backup

[dnanian]

Well, certainly Copy Newer would do a bit less stat-ing, but that stuff would likely be pretty cached. I don't think you'll see much of a difference...

Diagnosing will likely be quite difficult: you'd have to look pretty carefully about the pattern of I/O on the far side of the link, and I'm not sure you'd be able to make it much better without a lot of control of both sides.