> After looking at a few alternatives (Borg, Duplicacy etc.)

I may have looked at Duplicacy. I'm sure that I looked at one of Duplicacy [1], Duplicati [2], and Duplicity [3]. Whichever one that was, I kept getting it mixed up with the other two when looking for information online, and finally said "screw this" and bought Arq.

[1] https://duplicacy.com/

[2] https://www.duplicati.com/

[3] http://duplicity.nongnu.org/

Arq for Mac is great for backing up, though the restore util could use a little work. It's not exactly user friendly.

I've used it on my macs for years without any issues at all. I switched after Time Machine broke down for the n'th time in a month saying it needed to recreate the backup, and not once in the 3-5 years i've been using it has it every given me any problems with broken repositories, and every integrity check/restore has succeeded.

Arq on Windows is a different beast though. I'm sure it's technically solid, but the UI leaves a lot to be desired. On windows boxes i default to Duplicaty.

> Duplicaty

Did you mean Duplicacy or Duplicati?

Duplicati (https://www.duplicati.com/).

On my servers i use Borg like any sane person would, but the lack of a good client UI makes scheduling backups on a personal computer a lot more work than i'm willing to put in.

You would probably need the kernel / filesystem to keep track of it to keep it efficient. And even then that is iffy if you implement it as a kernel extension vs. something integrated into filesystem code.

I've found arq backup overall slow once you start hitting 0.5TB overall. It's a design issue.

> You would probably need the kernel / filesystem to keep track of it to keep it efficient

I believe most operating systems have a mechanism for this. E.g. on macOS it's called fsevents, Linux has inotify

Yes, these utilities would probably need something in them such that fswatch implements (https://emcrisostomo.github.io/fswatch/) - very useful.

I've been thinking about setting up a backup for my Mac for a while now. How long does it usually take to scan your folders during a backup?

I am backing up ~130 GB data (with a combination of large and small files) every 12 hours to S3. The first upload quite some time but all the later ones take ~10 minutes in total.