If things go wrong in a VMware vSAN 6.x environment you may see congestion warnings and errors – usually in hybrid setups. I try to explain what congestion means in the world of vSAN, why it’s a problem and how to deal with it.
What is congestion?
In short, congestion occurs when you have a bottleneck in the lower layers of your vSAN infrastructure. Or, more concretely: The destaging process of the incoming data, from the flash cache to the capacity disks, is so heavy that one layer of vSAN cannot handle this amount of data.