rhel8: how to manually migrate the root fs to a bigger disk?

oray

I booted with the recovery disk to migrate my production root fs to a bigger drive. While running with the recovery disk, I created 3 raid1 partitions on the target disk, one for the /, one for the /boot, and one for the /boot/efs. On these 3 partitions I created a raid1 array with only one component drive present thus making the array degraded at the outset. I tar'ed the production /, /boot, and /boot/efi filesystems and untar'ed them to their respective homes on the degraded raid1 arrays. I chroot'ed to the untarr'ed / file system and created a fresh initramfs and also ran grub2-mkconfig. Also fixed fstab with the new UUIDs. Now it is time to boot from the newly created raid1 disk. Booting fails because dracut cannot find the root fs. The root=UUID it is looking for is correctly referring to the newly created raid1 root filesystem. In the emergency shell ls /dev did not show the md device so I manually assembled it: mdadm -A /dev/md0 /dev/nvme0n1p3. Output of cat /proc/mdstat and madam --detail /dev/md0 all look healthy. I mounted the raid1 root fs on /sysroot and chroot'ed to it. I then terminated the emergency shell hoping dracut would continue. The monitor spewed some output that I could not catch and then dracut stopped dead.

oray

/etc/default/grub was missing "rm.md.uuid=the-uuid-of-roots" in the GRUB_CMDLINE_LINUX setting. Adding it and running grub2-mkconfig fixed the problem.