@elupus: Just tried but even setting it to 0.1 doesn't fix the issue on RPi. Only way is either disabling buffering or use SimpleBuffer (which is not a feasable option on flash based storage). Apparently RPi's RAM performance is terrible. Perhaps @popcornmix has an idea about this?

So for now I guess the only way to workaround this is this PR. One thing I'm still pondering about is whether it wouldn't make more sense (like suggested before) to make buffermode=0, disable all buffering?