How to expand a RAID 1 ?

[Enquiries]

Hi !

I'm a french photographer/videomaker and i have a question about RAID and NAS...

I currently have two 4To HDD in RAID 1. These two HDD are mounted on a HDD reader (like this : https://amzn.to/2R0n17e).

I want to buy a 4-Bay NAS and keep the two HDD that i already have and buy two more 4To HDD.

Is it possible to extend my RAID without loosing data from the two disks that i already have ?

I search on your site and youtube channel but i didnt find anything

I hope all is well for you in these complicated times.

Regards,
Michael