[rwmj]

This (and write performance) is one of the reasons why mkfs now defers initializing block groups until the drive is mounted. After mount the kernel initializes them slowly in the background. I did a talk which covers this:

https://rwmj.wordpress.com/2019/02/04/video-take-your-loop-m... (right at the end of the talk)

Just the graphics: https://rwmj.wordpress.com/2018/11/04/nbd-graphical-viewer/