1495MiB used raid6 in a VM using 4x qcow2 files on an SSD.
Host is using kernel 4.4.0
Guest is using kernel 4.5.0rc0.git9.1.fc24 (this is a Fedora Rawhide
debug kernel so it'll be a bit slower), btrfs-progs 4.3.1

Not degraded, balance takes 11 seconds, that's ~136MiB/s
iotop isn't consistent, max is ~300MiB/s write.

Reboot with 1 device missing and a new empty qcow2 in its place, mount
degraded and 'btrfs replace' takes 13 seconds according to 'btrfs
replace status'.

I don't know that this is very useful information though.

Christian, what are you getting for 'iotop -d3 -o' or 'iostat -d3'. Is
it consistent or is it fluctuating all over the place? What sort of
eyeball avg/min/max are you getting?


Chris Murphy