Acho que você precisava da reinicialização para o novo mapeamento da unidade de disco rígido a ser visto pelo sistema.
Se você quiser, pode tentar recuperar arquivos da 'superfície da unidade' com o PhotoRec,
link
ou veja o seguinte link,
Re: melhor maneira de limpar uma unidade
que também mostra a verificação do resultado com xxd
roten@my-precise:~$ sudo hdparm -I /dev/sdb
...
Security:
Master password revision code = 65534
supported
not enabled
not locked
not frozen
not expired: security count
not supported: enhanced erase
88min for SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 50000391f340058c
NAA : 5
IEEE OUI : 000039
Unique ID : 1f340058c
Checksum: correct
roten@my-precise:~$ sudo hdparm --user-master u --security-set-pass Eins /dev/sdb security_password="Eins"
/dev/sdb:
Issuing SECURITY_SET_PASS command, password="Eins", user=user, mode=high
roten@my-precise:~$ sudo hdparm -I /dev/sdb
...
Security:
Master password revision code = 65534
supported
enabled
not locked
not frozen
not expired: security count
not supported: enhanced erase
Security level high
88min for SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 50000391f340058c
NAA : 5
IEEE OUI : 000039
Unique ID : 1f340058c
Checksum: correct
roten@my-precise:~$ sudo time hdparm --user-master u --security-erase Eins /dev/sdb security_password="Eins"
/dev/sdb:
Issuing SECURITY_ERASE command, password="Eins", user=user
0.00user 0.00system 1:11:03elapsed 0%CPU (0avgtext+0avgdata 2432maxresident)k
0inputs+0outputs (0major+200minor)pagefaults 0swaps
...
Security:
Master password revision code = 65534
supported
not enabled
not locked
not frozen
not expired: security count
not supported: enhanced erase
88min for SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 50000391f340058c
NAA : 5
IEEE OUI : 000039
Unique ID : 1f340058c
Checksum: correct
roten@my-precise:~$ sudo time xxd -a /dev/sdb
[sudo] password for roten:
0000000: 0000 0000 0000 0000 0000 0000 0000 0000 ................
1000000000000 0000 0000 0000 0000 0000 0000 0000 ................
2000000000000 0000 0000 0000 0000 0000 0000 0000 ................
3000000000000 0000 0000 0000 0000 0000 0000 0000 ................
54272.57user 343.93system 15:10:36elapsed 99%CPU (0avgtext+0avgdata 2096maxresident)k
488398400inputs+0outputs (0major+179minor)pagefaults 0swaps
roten@my-precise:~$