Seems you flipped to the other side too far. It is of course more likely for an HDD to fail during heavy load times than during light load times. And rebuilding an array as large as 12x16TB takes a really long time. Depending on your RAID setup, the entire process might fail on a single unrecoverable read error during rebuild. With those settings, arrays of this size are almost certain to fail during rebuild. This tends to be the default setting for hardware RAID. If you can adjust this behavior to just accept the loss/corruption as a result of URE during rebuild, make sure you do.
That said, in general running RAID5 on such a large array is not recommended.
Have a look at this post and the linked article: