Are you running the latest firmware? It looks like 1 of the disks is giving issues, we also had this problem before.
I suggest you take a look at the disk which is located on PHY=2.
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Sometimes you can have drives that are failing, but not showing typical signs. Is the array speed pretty the same as it normally has been (writes and read speeds)? We've has issues where one drive was failing and causing a raid array to randomly crawl... but smartctl stats/etc all were normal.