Ty very much!
Just to mount system partition from livecd (pepermintos) i needed to use 'mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1'
The -U options didnt worked for me, i got "mdadm: No super block found on /dev/sda1 (Expected magic..."
Anyway.. Fixed now! TY AGAIN