[ceph-users] RBD latency

Good evening everyone! Guys, what to expect latency for RBD images in a cluster with only HDD (36 HDDs)? Sometimes I see that the write latency is around 2-5 ms in some images even with very low IOPS and bandwidth while the read latency is around 0.2-0.7 ms. For a cluster with only HDD is this latency expected? Is there any parameter I can study to improve? What do you recommend for tuning in the OS? The latency between machines is always around 0.1ms, all connected via fiber optics. Thanks in advance!