Unfortunately Synlology doesn't recognize a standard mdadm raid setup. The disks will be formatted once they're moved. So I had to figure out a way to move the data around.
I lucked out that I wasn't using most of my raid space. I have a Raid 5, 3x2TB and I'm only using about 1.5 TB of space. So any single disk will be able to contain all of the data in my raid.
I've posted this in the past, but my raid disks are sdb1, sdc1, sdd1.
mdadm --fail /dev/md0 /dev/sdb1
mdadm --remove /dev/md0 /dev/sdb1
mkfs -t ext4 /dev/sdb1
mkdir /media/transition
mount /dev/sdb1 /media/transition.
rsync -avP /media/raid /media/transition
Turn off computer, disconnect the drives and identify the disk that you've copied the data to.
The only disk that should be able to mount should be sdb1. Transfer the 2 disks to the NAS, as they will be erased shortly.
(Fair warning: You now only have 1 copy of the data, so I try to get this data migrated as fast as possible. single copy of data always makes me nervous )
If you haven't already setup rsync over ssh on your NAS.
If you have an external drive enclosure, connect the drive externally to your NAS and copy the data in, or the cheapsake solution is rysnc over ssh.
rsync -avP /media/transaition admin@nas-ip-address:/volume1/newRaid/
Step 7:
Convert raid 1, to a raid 5
Follow the instructions listed here