Debian grub2 and RAID1 degraided

dpkg-reconfigure grub-pc
cd /etc/initramfs-tools/scripts/local-top
cp /usr/share/initramfs-tools/scripts/local-top/mdadm .

 Replace

log_failure_msg "failed to assemble all arrays."

With this

 log_warning_msg "failed to assemble all arrays...attempting individual starts" for dev in $(cat /proc/mdstat | grep md | cut -d ' ' -f 1); do log_begin_msg "attempting mdadm --run $dev" if $MDADM --run $dev; then verbose && log_success_msg "started $dev" else log_failure_msg "failed to start $dev" fi done

At the end run this
update-initramfs -u