Inconsistent NetFlow control settings on vmnic ports used for iSCSI on the ESXi host

Products

• VMware vSphere ESXi

Issue/Introduction

• Latency is being experience on the configured iSCSI storage array.
• iSCSI aborts are also reported on the ESXI hosts.

Environment

VMware vSphere ESXi

Cause

The physical switch ports in which the ESX and the array interfaces are connected must have flow control enabled. Failure to do so can cause TCP level packet retransmits or iSCSI-level abort tasks.

Resolution

• All vmnics used for iSCSI must have the same speed on the ESXi host 
• All hosts in the cluster must utilize physical NIC adapters from the same manufacturer 
• All vmnics for iSCSI must operate with the same driver and firmware version. 
• Flow control should be enabled on the vmnics 

NOTE: Consult your storage vendor before enabling flow control to see if they recommend flow control to be enabled for when configuring iSCSI to their array.

Additional Information

Configuring Flow Control on VMware ESXi and VMware ESX