I want my device to still boot even if the array is degraded.

NOTE: this information may be outdated

Ubuntu

Configure mdadm

# /etc/mdadm/mdadm.conf

BOOT_DEGRADED=true

sudo update-initramfs -u

Configure grub

# /etc/default/grub

GRUB_CMDLINE_LINUX="bootdegraded=true"

sudo update-grub