This is a somewhat old LP bug, but for completeness it worth mentioning here that recently some patches were merged on initramfs-tools and cryptsetup, that allow a good experience booting with LUKS-encrypted rootfs on top of a degraded RAID1 array; for details, please check: https://bugs.launchpad.net/ubuntu/+source/cryptsetup/+bug/1879980
This is a somewhat old LP bug, but for completeness it worth mentioning here that recently some patches were merged on initramfs-tools and cryptsetup, that allow a good experience booting with LUKS-encrypted rootfs on top of a degraded RAID1 array; for details, please check: https:/ /bugs.launchpad .net/ubuntu/ +source/ cryptsetup/ +bug/1879980
Cheers,
Guilherme