Thanks Bill - thats what I was afraid of.
It ended up 5 by accident / lack of attention to detail I think - this filer is at our DR site and it’s also an office, our support guy there has been learning the NAS as a backup, we were moving all of his share data to the NAS from a file server and I told him to create an aggr with 5 disks, which he did and has done so before, the issue just came up when we needed more space, I went to add another disk and noticed the raid group issue. I guess he changed the raid group to 5 thinking it was the number of disks, and he apparently added three disks on his last expansion. I went back and checked all the other he has done and they are correct – not paying attention I guess.
Yes a way to reallocate disks / RGs or shrink aggrs would be nice. I have several times needed to shrink / recover disks from an aggr after a project is over but there is just a little bit of data remaining, so I have a catch-all aggr that I mirror the last bits to until they can be deleted so I can blow away the original aggr. Not hard just time consuming - easy to give, hard to take back.