Hello HornHead,   It is going to be a switch setting and not a storage setting. You'll want it on, on the switch port that has the storage connected.   Reference the Support Matrix for both storage in the rules section: ME4 Support Matrix Page 7 : [URL] ME5 Support Matrix Page 7: [URL]  
Per this best-practices page here for the ME4 and ME5, they both say this: We recommend the following settings when enabling flow control: So the usage of the word "minimum" made me curious as to whether Dell would actually recommend MORE than just receive - that actually, Dell is saying that if our switches support it, they are recommending enabling both receive and transmit flow control. So I want to confirm - both the ME4 and ME5 support symmetric, receive and transmit flow control, not just receive? We are coming from a compellent which only supported receive.
Do the Powervault ME4 and ME5 series support both receive and transmit flow 
control?