Let’s assume ! on a nice sunny day , you receives complaints that your Ceph storage cluster is not performing as it was performing yesterday. After checking cluster status you found that placement groups scrubbing is going on and depending on your scenario , you would like to decrease its priority. Here is how you can do it.
Note : OSD disk thread I/O priority can only be changed if the disk scheduler is cfq.
Check disk scheduler, if its not cfq you can change it to cfq dynamically.