I have quite a large IO wait showing in top. I suspect this is fault of SDA drive (on of 2 disks in RAID array), which was replaced about week ago. There are no errors visible, smart showing nothing, but disk SDA in atop is always a lot more busy then SDB. SDA is not rebuilding, so that's not the problem.
It seems the problem it not with writes, but with reads only.
I would like to force RAID to read only from one disk, SDB, to check if it's going to work better. Is it possible to force RAID to read only from SDB, while still write to both?
I'm using a software Linux MD RAID on CentOS 6.0.