Recover data from accidentally created raid5 over raid1

[Moritz Rosin <moritz.rosin@itrosinen.de>]

Hey there,

unfortunately I have to admit, that I learned my lesson the hard way 
dealing with software raids.

I had a raid1 running reliable over month using two 4TB HDDs.
Since I ran short on free space I tried to convert the raid1 to a raid5 
in-place (with the plan to add the 3rd HDD after converting).
That's where my incredibly stupid mistake kicked in.

I followed an internet tutorial that told me to do:
mdadm --create /dev/md0 --level=5 --raid-devices=2 /dev/sdX1 /dev/sdY1

I learned that I re-created a raid5 array instead of converting the 
raid1 :-(

Is there any chance to un-do the conversion or restore the data?
Has the process of creation really overwritten data or is there anythins 
left on the disk itself that can be rescued?

Any help would be appreciated. Thanks!!!

Moritz