Back in the day best practice would be to mirror all drives on different shelves with drives from different batch and different power supply for each shelf.
The definitive guide to RAID is at http://www.baarf.dk/BAARF/BAARF2.html
About 25 years ago I witnessed a classic RAID 5, 5 disk failure. Every day for a week one drive went down and was replaced the next day. At the end of the week the recovery had not quite caught up. Spectacular.