QoS is a means to ensure specific performance levels for applications and workloads. There are two ways to accomplish this:
1. Ability to set limitations to avoid unwanted behavior from non-critical VMs.
2. Ability to set guarantees to ensure service levels for mission-critical VMs.

vSAN currently supports only the first method and focusses on IOPs. "MBps Limits" cannot be set. It is also not possible to guarantee a certain amount of IOPs for any given VM.