[dnanian]

Destination drives, just like source drives, can go bad. And Disk Utility/Warrior/etc don't test the drive surface. They check the drive structure, but don't try to read/write files.

In this case, the data area went bad... and zeroing found and re-mapped that.

Can you trust the drive? All drives have bad areas. But, usually, the drive re-maps them "automatically". In this case, it might not have had any more spares, so the drive couldn't remap transparently.

Zeroing will typically test everything and so it's good... for now. But if you end up with another problem, I'd replace the drive.