Cannot expand storage pool

[BuckHunter]

I have a TS-453Be that I had 4 8TB drives in. Had one of the drives go bad and another showing warnings so I replaced both of them with 16TB drives (I was needing more space also). When I view the pool, it shows I can expand it to 14TB available space (from 11TB) but I don't find any option to expand it. When I go to the "replace drive by drive" option, the expand size is greyed out, even after I have replaced both drives and the raid rebuild has completed.

Do I have to replace all 4 drives with 16TB drives for it to expand or can you do it with 2 at 8TB and 2 at 16TB?

Any recommendations on how to get more space with a setup of 2 8TB and 2 16TB drives?

[dolbyman]

Unclear what the RAID setup is..but unless you run two RAID1 ..you cannot expand the space with 2 groups of different size drives..ALL drives will have to be swapped to expand

[BuckHunter]

It is a RAID 6 setup.

Based on what I'm reading, using that raid setup, I would need to have all 4 drives the same size.

[dolbyman]

correct