Ran out of space on WD PR2100

I have a WD PR2100 with 12tb in RAID 1 configuration and I ran out of space. Aside from switching to RAID 0, any ideas on cost effective way to go? I would prefer to not to have multiple NAS drives and have to switch between them to see what I have on PLEX Media app… I use my NAS 100% for movie storage running PLEX.

Upgrade all four drives with 10tb and you will be good to go.

Probably the least helpful answer I’ve seen on here. Besides, the PR2100 only has two bays!

Maybe consider buying a PR4100 with enough storage space to suit your needs. You could then easily transfer your data across, then sell the PR2100 to recoup some cost?