NAS unavailable after disk swap (Raid 1)

[Remkon]

Hello,

A while back I started to upgrade my Asustor from 2tb raod 1 to 4tb raid 1.
After swapping the first disk the raid started syncing the disk and everything was fine.
Now im trying to hotswap out the other 2tb disk for a new 4tb disk but as soon as i remove the 2tb disk the nas becomes unavailable, when I restart the nas it acts as if its a brand new nas and it wants to wipe the disks.
When I put back the 2tb disk the raid set starts syncing again and everything is fine.

I have tried to place the 4tb disk with data on it in slot 0 but no luck. I have tried to shutdown the nas before swapping the disks but it then also acts as a new nas.

It looks to me that there are certain config files stored on the 2tb disk that somehow arent mirrored to or are corrupted on the other disk.
Both disks do not show any errors.

I dont want to lose data obviously so I'm kinda stuck right now.

I'm going to copy my important data to my old synology in case there's no other option than whiping and starting over, but I much rather have it solved.

Anyone got this before?
Thanks

Edit: forgot to mention that i get an internal server error when i try to browse to the nas and in asustor control center the status shows as 'blocked'

[orion]

Did you wait for sync task competed after you replace disk-1? Normally it should take several hours or days (depends on disk size). After done, volume should show status ready (it means RAID-1 is working fine to protect your volume). After that, you can replace another disk.

[Remkon]

Yes, I did wait, it takes about a day to sync and will say that I can have 1faulty disk.

I kinda wonder whay will happen if i replace the new 4tb disk with the other 4tb disk, have it sync and then swap the 2tb foe the 4tb. But then again I need the raid to work properly otherwise there's no point in having a raid1 setup.

[orion]

Then, there should be something wrong which I don't know. I think you'd better to ask asustor to check it remotely. https://support.asustor.com/

By the way, your original data should be safe in case that your original disks (disk-1 and disk-2) are still keeping the same (i.e., not write any data yet).