Indeed! Fortunately the RAID was also backed-up offsite. But, the entire process was shocking in several ways.

At least Samsung was fairly speedy with the RMAs and it was basically no-questions-asked... because I imagine they're getting tons of these mailed back to them.

Did they require the failed drives to be returned? Did the secure erase function work on a failed drive? I guess this is a good reason for full disk encryption even on machines where I'm satisfied with their physical security.

Yes, they sent a prepaid label to return the bad drives. I did a secure erase both via Linux command line and via their proprietary software and it seemed to work. The whole process took about 3 weeks per drive.