I have a very slow disk. So I tried to increase dirty buffers
/proc/sys/vm/dirty_background_bytes:0
/proc/sys/vm/dirty_background_ratio:50
/proc/sys/vm/dirty_bytes:0
/proc/sys/vm/dirty_expire_centisecs:60000
/proc/sys/vm/dirty_ratio:80
/proc/sys/vm/dirty_writeback_centisecs:500
DDing a 5 GB...