User`s guide

PLANNING FOR HYPER-V
November09 Page11 
gigabit Ethernet networks are designed to always have auto negotiation enabled. If a
particular application requires a specific speed or duplex mode, you can accomplish
this by changing the advertisement options of the switch.
SpanningTreeProtocol
Disable the spanning-tree protocol (STP) on the switch ports that connect end nodes
(iSCSI initiators and storage array network interfaces). If you still decide to enable
STP on the switch ports, turn on the STP FastPort feature on the ports to allow
immediate transition of the ports into forwarding state.
Note: FastPort immediately transitions the port into the STP forwarding mode upon
linkup. Because the port still participates in STP and it is to be a part of the
loop, it eventually transitions into the STP blocking mode.
Note: PowerConnect switches default to Rapid Spanning Tree Protocol (RSTP),
which is an evolution in STP that provides for faster spanning tree
convergence and is preferable to STP when available.
Note: Use STP for a single cable connection between switches or for trunking for
multiple cable connections between switches.
TCPCongestionAvoidance
TCP congestion avoidance is an end-to-end flow control protocol that limits the
amount of data sent between a TCP sender and a TCP transmitter. This protocol
uses a sliding window to size the data being sent to the TCP receiver. This protocol
starts with a small segment size and keeps increasing with each acknowledged
segment sent until a segment is dropped. After a segment is dropped, TCP starts
this avoidance over again.
EtherFlowControl
It is best practice to enable flow control on the switch ports that handle iSCSI traffic.
In addition, if a server is using a software iSCSI initiator-and-NIC combination to
handle iSCSI traffic, enable flow control on the NICs to also obtain a performance
benefit. In SAN configurations in which many servers (initiators) are communicating
with storage devices, if senders transmit data simultaneously, the data transmission
might exceed the throughput capacity of the receiver. When this event occurs, the
receiver might drop packets, which forces the senders to retransmit the data after a
delay. Although this event does not result in any loss of data, latency increases
because of the re-transmissions, and I/O performance degrades. By enabling flow
control, you can avoid the imbalance in the network traffic between the devices that
send network traffic and the devices that receive the traffic.