It’s technically both! There’s a max drive count, max capacity as well as a max aggr size. And depends which limit you hit first when it comes to the max drive count and max capacity count. if you have 144 drives on your 2554 you’ve hit a limit. But say those drives are 10TB and not 2TB. You could go over the max capacity count of the system.
there’s also max aggr count, etc etc. ONTAP is all software raid. All maxes can be found at Hardware U. Http://hwu.netapp.com
Storage eff doesn’t matter if the aggr can write 100TB, then it can write 100TB. If 300TB of data get written in there using dedupe. That’s a great 3:1 storage eff.