This is a small history of changes we saw in a customer situation with several performance issues in a VMware environment.
In the beginning the customer had Buffer Credit Waits of more than 51%. 

This means that in the timeframe (5 minutes every morning – see needles) the SAN was only available half of the time to accept writes.

We gave the customer 3 tips to improve this situation

1. Rebalance the load on the node ports
2. Reduce SAN traffic between the SVC nodes – do not address the “non preferred node” in this case
3. Increase switch port buffer credits for the SVC connected ports from 8 to 41 

see what happened after the changes have been implemented

Solved Buffer Credit Wait situation at a customer side