I received a very good question this week to which I did not have the answer, I had a feeling but that is not enough. The question was if Storage vMotion would be “throttled” by Storage IO Control. As I happened to have a couple of meetings scheduled this week with the actual engineers I asked the question and this was their answer:
Storage IO Control can throttle Storage vMotion when the latency threshold is exceeded. The reason for this being is that Storage vMotion is “billed” to the virtual machine.
This basically means that if you initiate a Storage vMotion the “process” belongs to the VM and as such if the host is throttled the Storage vMotion process might be throttled as well by the local scheduler(SFQ) depending on the amount of shares that were originally allocated to this virtual machine. Definitely something to keep in mind when doing a Storage vMotion of a large virtual machine as it could potentially lead to an increase of the amount of time it takes for the Storage vMotion to complete. Don’t get me wrong, that is not necessarily a negative thing cause at the same time it will prevent that particular Storage vMotion to consume all available bandwidth.