I don’t know if there is a (of the shelf) DAS out there that supports using drives with existing data on them and also some additional drives with RAID in the same enclosure.
In case you don’t have some place to store the data temporarily you can just use it as it is and save SE money for a NAS.
Because I am asking myself: if you don’t have a place to store the data temporarily, where is your backup? Sounds like you don’t have one. In this case you can save for the NAS AMD use the external drive as a backup drive attached to the NAS. Win-Win maybe?



OK, then maybe a DAS where your can put your drives in and also add some additional ones. Attach it to one of your Servers and Expose them via smb/NFS.
So something like @agile_squirrel@lemmy.ml and @Ugurcan@lemmy.world mentioned.