Comment # 36 on bug 1169774 from Jan Kara

If this is happening on both ext4 and btrfs it seems unlikely to be caused by
ext4 specific problem (provided btrfs ever worked before). But anyway, let's
debug this and we'll see where the problem is. The difference between XFS and
ext4 shouldn't indeed be that big.

Now I'm mostly ignorant of OBS (well, I use it to build simple packages but
that's all). So if I understand right 'vmfstype' influences what is used as a
root filesystem of the VM that is doing the build of the package? I.e. in your
case of live CD images?

What exactly happens between installation of kbd-legacy-2.3.0-1.1.noarch and
kernel-firmware-20201023-1.1.noarch in the build system? This is the difference
you care about right? But even in the "fast" case it takes 23 seconds so I'd
like to understand what the system is doing during this time... Also where can
I see the full logs you've pasted from?