Late to the party, but “me, too”. I encountered the same issue with (2) Toshiba X300
Since I did not want to take the drives out of the Turris Omnia NAS, I only took the cover off, left the drives powered by the Turris Omnia, and connected internal SATA cables from a desktop machine. From the desktop machine, I was able to zero the drives (in parallel). Once that was done, I disconnected the drives from the desktop machine and reconnected everything in the Turris Omnia. Then, I was able to mdadm --create --assume-clean --level=raid1 … , and mkfs.ext4. After that, I have not had issues accessing the drive over samba from a single client, but I am hesitant to try and put excessive load on the box, especially since CPU temperature was sustained at119°C while the single client was copying a few hundred GB over samba (as noted in Operating temperature - #74 by pgotze - Omnia HW help - Turris forum)