I have three external 4 TB drives in a #ZFS RAID-Z1 for backups.

Recently, one of the drives failed I think primarily due to heat. I replaced that drive today, but decided I wanted something to manage the heat a bit better.

My employer had some aluminium scraps that I could rest the drives on, lifting them off the desk, improving airflow. But being aluminium, they'll also absorb any heat the drives put out.

I also put a USB fan above the drives for cooling. Hopefully this improves lifespan.