Usn-policy=on nearly doubles backup time

I’ve been experimenting with options to try and make the backup run faster. I’m currently on 1h15 for a 125GB backup, but it includes hundreds of thousands of files.

disable-file-scanner=true reduces the cpu usage by half but doesn’t make a speed difference, use-block-cache=true didn’t make any difference, and usn-policy=on actually slowed it down to over 2 hours (no log warnings).

Is the option not ready for use yet? I let it run 5+ backups before I switched it off, so it had a chance to remember the previous runs. It seems it should be the most useful option, and it’s obviously doing something, just not what you’d expect it to do.

If there’s any other suggestions too please let me know, I’m still transitioning from CrashPlan so I like the idea of a more “live” backup. The biggest speed increase I found was using a single regex string instead of multiple lines. I got a test 1TB backup down to a 15m scan after it was originally taking 2h30.

Using Information level (rather than the default Warning level that a log file uses) might reveal more.

It seems good, but not perfect. There are known TODO items, according to Real-time backup. More:

You can do your own research, but usually people complain of its slowdown when it DOESN’T run.

USN option working inconsistently talks about soft failures (reported in the log at Information level).
Logging changes to be more specific are also mentioned there. But it’s not clear if this is your case.
Possibly this is just a your-mileage-may-vary situation. Your USN “seems” like it’s doing something.

I am not a USN expert, so I can mainly point to technical discussion from original author and others.