1. When installing Ubuntu, configure both disks as boot devices, create two RAIDs, but do not create
partitions on RAIDs (format md0 as root, md1 as /RAID0). Use Linux as usual, pray disks do not die.
2. If one disk dies, Ubuntu should boot from another one, hang for 1.5 minutes on startup of /dev/md1.
Wait till it boots, comment out /RAID0 in /etc/fstab and reboot. Linux should work from /dev/md0 without
problems.
3. If you decide to add another disk, after boot, copy partition table:
 sfdisk -d /dev/nvme0n1 | sfdisk /dev/nvme1n1
When, copy BIOS boot partition with dd:
 dd if=/dev/nvme0n1p1 of=/dev/nvme1n1p1
When, add spare partition to md0:
 mdadm --add /dev/md0 /dev/nvme1n1p2
RAID0 has to be recreated from the start:
 mdadm --create /dev/md1 --level 0 --raid-devices=2 /dev/nvme0n1p3 /dev/nvme1n1p3
Update /etc/fstab to use new RAID0.
Create new mdadm.conf:
 mdadm --details --scan > /etc/mdadm/mdadm.conf
Update initramfs:
 update-initramfs -c -k `uname -r`
Install grub to the new disk:
 grub-install /dev/nvme1n1
 update-grub
After reboot, Linux should work without problems. It may also survive the death of any of two disks again.