We have a Linux server with a RAID 1 using two HDDs on which runs a Apache server managing multiple sites and some other services that interact intensively with the databases and produce massive amounts of logs. Because the drives are not SSD but HDD, the databases is becoming very big and the I/O load is very high on the server, the database performance is very bad. We managed to make our hosting company to add to the server two HDDs.
Now I have two questions:
What's the best setup for the server to increase I/O performance? I thought it would be better to put the two added HDDs into an another RAID 1 array and to move only the MySQL database to the new RAID device. That way the database would not be affected by other factors such as high quantity of logs produced by some services. Are there any better options? (OS re-install is not an option and I need the least possible down-time)
Is it safe to do so? Are there risks of data loss if moving the entire MySQL data directory to another device? (I know how to do this)