There was also a failure mode in Seagate drives where the bearing increased in stiction. As long as it was spinning, there was no problem. But if you spun it do

There was also a failure mode in Seagate drives where the bearing increased in stiction. As long as it was spinning, there was no problem. But if you spun it down, it might not spin up again. If you had a group of disks powered up for a long time, many could fail together at the next power cycle. A chaos monkey that randomly powers down disks one at a time can prevent this.