Is this problems happens on all drives or only on some of them ?
-Is there some drives where the problems happens more often ?
-Where are located all the drives ?
-Are they all in the same electrical room ?
-When do this problems happens ? (beginning of campaign, end of campaign, etc.)
-What is the temperature in the electrical room ?
-Are the electrical room and drives are clean ? (no condensation, no sugar dust)
-Are the fans in the drives are working well ? (blowing in the good way ?)