Dependent Hardware iSCSI Considerations

When you use dependent hardware iSCSI adapters with ESXi, certain considerations apply.

• When you use any dependent hardware iSCSI adapter, performance reporting for a NIC associated with the adapter might show little or no activity, even when iSCSI traffic is heavy. This behavior occurs because the iSCSI traffic bypasses the regular networking stack.
• If you use a third-party virtual switch, for example Cisco Nexus 1000V DVS, disable automatic pinning. Use manual pinning instead, making sure to connect a VMkernel adapter (vmk) to an appropriate physical NIC (vmnic). For information, refer to your virtual switch vendor documentation.
• The Broadcom iSCSI adapter performs data reassembly in hardware, which has a limited buffer space. When you use the Broadcom iSCSI adapter in a congested network or under heavy load, enable flow control to avoid performance degradation.

  Flow control manages the rate of data transmission between two nodes to prevent a fast sender from overrunning a slow receiver. For best results, enable flow control at the end points of the I/O path, at the hosts and iSCSI storage systems.

  To enable flow control for the host, use the esxcli system module parameters command. For details, see the VMware knowledge base article at http://kb.vmware.com/kb/1013413

• Dependent hardware adapters support IPv4 and IPv6.