Avira Windows Antivirus Scanner slowing Restic (aka "Why is restic slow and using a lot of disk on Windows")

[wscott]

FYI the same thing happens with Windows Explorer and the same workaround fixes the problem: Add rustic.exe to the list of excluded processes.

Windows Defender causes 10X+ slowdown

So I have been playing with having a nightly backup job scheduled on my Windows 10 laptop using Task Scheduler. Now that Windows 10 includes SSH it is getting easier to do. But I was surprised my backup of a 4GB directory was taking 2m30s to do a scan when nothing changed. Poking around with Task Manager I find that the Windows Defender malware scanner is running and taking up the time. When I disable “Real-time protection” the time to run my null backup drops to like 10 seconds. The only th…

I still find it very strange that whatever restic is doing causes the virus scanners to think files on the disk might have changed. Other programs can read every file in a directory without causing the virus scanner to run.

As I understand it, restic should be reading the directory entries and then calling the moral equivalent of fstat() on each entry. (1) This shouldn’t be interpreted as changing files by the virus scanner so it is strange.

---

1. Calling fstat() on every scanned file is a known outstanding performance bug in the scanning code, but lower priority than the issues with restore or prune.