If you want a workload that has 50% 2k reads and 50% 4k reads, while
having 90% 4k writes and 10% 8k writes, you would specify::
- bssplit=2k/50:4k/50,4k/90,8k/10
+ bssplit=2k/50:4k/50,4k/90:8k/10
Fio supports defining up to 64 different weights for each data
direction.