Initialise the superblock if you reuse hard disks

WARNING! If you are using hard disks which have a md superblock from an earlier installation in a different RAID array, you MUST zero the superblock before activating the
autostart feature.

For doing this, do not start the RAID devices automatically and zero the superblock (mdadm --zero-superblock /dev/xxx). You can then further use 'dpkg-reconfigure mdadm' to
activate the autostart feature.

If RAID devices are started automatically, all RAID devices are discovered and assembled automatically at system startup. This option should only be used if the md driver is
compiled as a module. If it is compiled into your kernel, the automatic startup will be performed at boot time by the kernel and therefore you should not choose this option.

Do you want to start the RAID devices automatically