A new array needs the same file: it is created and recorded in mdadm.conf right away.
mdadm --create (in the Wiki) builds an array: the device name, the level, the number of disks and the disks themselves. Before creating it, mdadm warns that an array with metadata at the start of the disk may not suit /boot and asks Continue creating array? — for a data array answer y. The --run option answers the question by itself.
The application's logs need a second mirror, and mdadm.conf already lists the data array.
Build a second mirror
The logs need a second mirror. Build a RAID 1 array /dev/md1 from the new disks /dev/loop3 and /dev/loop4 and record it in /etc/mdadm/mdadm.conf, which already holds a line for the md0 array.
Goals · 0 of 2
- Build the md1 mirror from the two new disks not done yet
- Record the new array in mdadm.conf not done yet