I have a TS-219p. Had 2 X 1tb drives mirrored. Wanted to upgrade to 2 X 2tb. Change one disk to 2TB hoping it will mirror and then I can update the other one. It didn’t and it ended up with an empty disk, luckily I had taken backup. Put the second disk in and copied everything from the back up and added more data from other nas drives. today I realised that they may not Mirrored as it say disk 2 not mounted and gives me option to format it. How can I add this disk as a mirrored to disk?
Can you post some screenshots?
On these old NAS is mostly easier to start from scratch
yeah two single disks
just erase both disks (diskpart / clean) and start the NAS from scratch as RAID1
The suggestion to start fresh is likely the best and most reliable way.
However using your original disks I believe would also work (but perhaps introduce some legacy issues), if you follow the guide to replace the disks 1 by 1. There is a specific process, not just inserting new drives and hoping for the best 
Thanks for the reply. But we have already copied more than 1tb on it. If this the only way then so be it. I have another request which I’ll start a new case but I ask you first. We have an old system which runs on XP. There is no new development on the software which makes us one of the few people who can do this. I cannot map to our TS-219p, any ideas??
XP default SMB level is 1.0. So there should be no issue.
But in any case enable SMB2