From 2x2TB and 2x1TB to 4x2TB: Only 4625GB available

OK, I had wondered why there was no Respriping information came up after changing the first disk. Only resync started. But I did not care about, because I just changed the first 1TB to a 2TB disk. After i changed the second disk respriping information came up.
But now I have fear about my data. How could all data be not corrupt, when disk 1 isn't used? (At the time I changed the second disk).

I will check if removing and reinsering will help ...

Many thanks to you! (I know why I still use Netgear !)

Disk 1 is used for /dev/md2 (the first layer on which your data volume resides) still. It just hasn't been used for vertical expansion. That's why you had less expansion than anticipated.

And you think a manual removing will help? Or should I first delete all data before I put the HDD back?

Manual removing and reinsertion while the NAS is on may help. The disk will be wiped and added back into the array.

Now the resync and resprining finalized! And now I received the message : extended to 5553 GB!

Thank you very much! You solved it.
You can close this post now.