Amazon web services – AWS EBS io1 IOPS pricing

My AWS EC2 application systematically requires about 3000 IOPS, but only about 100 GB of disk space. Comparing prices between gp2 Y io1 It looks like (from for Ohio):

  • gp2: 1000GB of disk would cost $ 100 / month ($ 0.10 / GB-month * 1000GB). There would be 90% wasted disk space, but I would get my 3000 IOPS sustained.
  • io1: 100GB of disk + 3000 IOPS would cost $ 207 / month (0.065 / IOPS-month * 3000IOPS + 0.125 / GB-month * 100GB).

Am I doing the right calculations? Is it really 2 times more expensive to get a smaller disk with the same IOPS in io1? It seems that there would never be a reason to use io1 and instead, enough gp2 Disk space to get IOPS for free. Am I missing something?