Can I create a "soft" RAID1 array without nuking data?

I've just bought two 1.5TB disks with the aim of creating a 1.5TB RAID1 array.

In my infinite lack of wisdom (and a lack of space inside the computer - it already had 6 disks), I stuck one in, formatted it to EXT4 and proceeded to copy data all over it from drives that I'm subbing out.

Now I want to create a mdadm RAID1 array with its twin disk. I thought this was possible. Probably involving unmounting and dding the content across but I'm sure I saw this somewhere before...

But I can't find the tutorial I used the last time I was setting up mdadm so I'm scared. I don't want to nuke 800gigs of data.

Solution 1:

You're most likely talking about this http://www.debian-administration.org/articles/238

"Now use mdadm to create the raid arrays. We mark the first drive (sda) as "missing" so it doesn't wipe out our existing data..."