My NAS killed the drives after 'ERASE' command

i have had issues with this NAS and disk capacity, had 2 x 2tb and 2 x 4tb. have finally figured out and understood the interesting way netgear try and hide their raid setup, as only had 6tb of space and expected more

so moved 4tb discs to bay 1 and 2, and 2tb to bay 3 and 4

after several factory resets it stubbornly refused to forget about the volume, so i deleted the volume using the NAS menu "ERASE"

erases, fine, counting, says it will reboot when done

THATS when it goes haywire. it has never rebooted properly with the discs in it

i have tried several ways, i can get it to boot with 1 disc, but when i try to create a volume it fails saying cannot access - fsync error

i have put the discs into a windows PC - BIOS detects, but when i try any program to fdisk etc i get "cannot initialise disk"

i have even tried a linux distribution to install, and same fsync error

so the BIOS detects the drive correctly, but somehow the disks are toast - all 4 i cannot access, fdisk, format, nothing so far

suggestions for any tools i may not have already tried? i am astounded, and stumped

firmware is 5.3.13 all latest available. all i did was follow the porcedure and this