In this post Chris writes about Storage I/O control in Cloud offering and on Storage arrays:
QoS on Storage
To my knowledge, today only SolidFire offers a storage array capable of delivering quality of service for I/O. All other devices aim to deliver IOPS as fast as possible, usually with little prioritisation to the results (other than first in, first out). Storage in the cloud needs to be more flexible and more intelligent, potentially using intelligent storage arrays as the underlying hardware platform. As usual, Amazon seem to be taking the lead (even if they are doing it with home-grown solutions), a one surely the others will simply follow, rather than innovate.