Has the SA6400 finished checking the drives?
I suspect RAID F1 may be the problem. Can you check if these commands return in_sync or writemostly
cat /sys/block/md0/md/dev-sata1p1/state
cat /sys/block/md0/md/dev-sata2p1/state
cat /sys/block/md0/md/dev-sata3p1/state
cat...