I just found this vmware knowledge base article in the web
I think one of the solutions to this problem can be found in the behavior that we have described here
The bad thing for this is - you will probably not see this problem when you cannot go deeper into the system.
Performance Analysis VAAI undercover write operations
Performance Bottleneck Analysis- VAAI undercover write operations
In this example we will see that the usage of the VAAI is somehow hidden from ordinary monitoring methods because the VAAI data streams are not visible on the top SCSI layers. So it might look like a system reacts overloaded without any reason but the reason can be uncovered when you look deeper into the system when your analysis tool is tailored good enough to SVC/Storwize and enables you to see needed the performance indicators.