This tip assumes that you have two disks that have equal sized free partitions that can be used.
RAID 1 is commonly referred to as mirroring. Every bit that is written to disk 1 is also written to disk 2, so in the event of a failure of disk 1, disk 2 has a complete mirror of all data and you can keep right on going. To create a RAID 1 mirror of two partitions, run the following
mdadm –create –verbose /dev/md0 –level=1 –raid-devices=2 /dev/$DISK1 /dev/$DISK2
Where $DISK1 is the first partition (sda1 for example) and $DISK2 is the second partition (sdb1)
To verify that worked, cat /proc/mdstat