I forgot to mention that after creation of md2 I've added a new line to /etc/mdadm.conf: # cat /etc/mdadm.conf DEVICE partitions MAILADDR root ARRAY /dev/md0 level=raid1 num-devices=2 UUID=91518bd3:79953138:f203f159:f2795fde ARRAY /dev/md1 level=raid1 num-devices=2 UUID=5b6722ca:b325344b:4ab40fc6:c3f1d6b4 ARRAY /dev/md2 level=raid1 num-devices=2 UUID=45e2f59b:1be94f42:5d55c385:da4faf78 # mdadm --examine --scan ARRAY /dev/md0 level=raid1 num-devices=2 UUID=91518bd3:79953138:f203f159:f2795fde ARRAY /dev/md1 level=raid1 num-devices=2 UUID=5b6722ca:b325344b:4ab40fc6:c3f1d6b4 ARRAY /dev/md2 level=raid1 num-devices=2 UUID=45e2f59b:1be94f42:5d55c385:da4faf78 -- Tomasz