Regarding write back cache: Disabling the write back cache won't have a real large impact on the endurance of the drive unless it reduces the total number of bytes written (which it won't). I've seen drives that perform better with it disabled and drives that perform better with it enabled. I would test in your environment and make the decision based on performance.
Thanks. I assume you are referring to the write back cache on the RAID controller here and not the disk cache itself.
