NB: You either need to be logged in as root, or use sudo to do all this...
- Use your favourite editor to create or edit /etc/mdadm/mdadm.conf file as follows:
If the file does not even exist, paste the following into the new, empty file:
# Please refer to mdadm.conf(5) for information about this file.
# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes
# automatically tag new arrays as belonging to the local system
# instruct the monitoring daemon where to send mail alerts
# definitions of existing MD arrays
This should add a line like the following to the end of mdadm.conf:
ARRAY /dev/md0 level=raid5
If the mdadm command has added any other stuff above the ARRAY line, remove it. For example, on one of my machines, the command returns 'mdadm: metadata format 00.90 unknown, ignored.' before the ARRAY line.
Your array should now auto-build on boot and thus you can add an entry to /etc/fstab to mount it (if it's not already there)