mysterious load on server due to mysql
Please pay attention to the raid status: VERIFYING. The progress is displayed as %V/I/M. You can see the verify schedule with the show verify command parameter. As long as the raid is being verified I assume the io performance isn't great. You should use iostat or vmstat to get a better picture what is happening.

The cache is enabled for your raid unit. You might want to test if the overall performance is better if you only enable the write cache but disable the read cache
Furthermore the bbu status seems to wrong - the battery has 0 hours estimated backup capacity.