I'm periodically establishing short SSH connections to one of the local servers. I observe intermittent timeouts. After investigating the issue, I found that SSH timeouts happen when there is a lot of IO write activity to the server's RAID array. What happens is that SSH connection "hangs up" for the duration of that write burst.
The server has plenty of available user memory (18 out of 64GB), swap space, and its CPUs are definitely not overloaded.
a normal behaviour
indicates some RAID hardware problem
something is not configured properly