[anarazel]

I'd hope that their data is all encrypted at rest. Compared to the bandwidth of spinning disks, the cost of doing hardware assisted AES isn't big.

[m4rtink]

Yeah, I would expect any data reaching the drives to be encrypted by Backblaze, with the key newer reaching the disk.

You could even have keys per disk and wipe them when a disk fails.

Either way, you should be fine to RMA the drives as for an external observer without the keys they just contain random noise.