I have set up a system with /dev/sda as its only disk.
I want to avoid any downtime and unplanned surprises (disks deciding to die) so I thought I'd set up the system in a RAID1.
So I need to:
Copy the partition table from sda to sdb
Create the disk array with the new disk and a missing disk
Create filesystems on the new partitions (sdb)
Set up mdadm
Copy the data from...