raid-1: increase rebuild speed on current rebuild

Question

I see my raid-1 array rebuilding (first time after adding 2nd partition) and want to increase speed

SO I set

echo 100000 > /proc/sys/dev/raid/speed_limit_min
echo 400000 > /proc/sys/dev/raid/speed_limit_max

but it's still around 18000 K/s

md1 : active raid1 sdf1[2] sdc1[1]
      1953514432 blocks [2/1] [_U]
      [>....................]  recovery =  2.8% (56107456/1953514432) finish=1675.6min spe
ed=18871K/sec

Does the changes take place only on new started rebuild? But is it possible to "restart" interrupt/continue a rebuild?

I have to add the disks are usb (2.0) disks and i have no clue how fast my usb usually is or should be.

Answer 1

The USB drives should max out at between 20 and 25 MB/s. If both your USB drives are on the same root hub that speed will be divided between reading and writing. Even on two separate root hubs the latency of reading from one drive then writing to the other would cause a delay meaning you won't get the full speed.

18 MB/s is actually not that bad a speed for USB under such conditions.