Each EBS volume can be modified once every 6 hours. I did not know it until 5 minutes ago. I resized a EBS volume from 100G to 150G, then I thought it might be better give it more space. To my surprise, I got this error when I tried to resize it again to 200G.
Continue with yesterday's good news, another exciting new feature on EBS - Elastic Volumes. It allows you to dynamically increase capacity, tune performance, and change the type of any new or existing current generation volume with no downtime or performance impact. Check it out: https://aws.amazon.com/ebs/details/#elasticvolumes