The problem is common to virtually all non-managed gigabit switches. The expected behavior in this configuration is for the sender's gigabit bandwidth to be divided between the two receivers.
Each receiver would lose some throughput due to the overhead of the simultaneous tranfers. But both would still function at speeds near those experienced when running solo. But what readers have reported are instances of gigabit links being forced to Fast Ethernet speeds. One reader said that merely plugging a NIC running at Mbps into a gigabit switch was enough to force all gigabit links to Mbps speed. But the more common scenario requires simultaneous transfers from a single gigabit machine to a mix of gigabit and Mbps computers.
Once a helpful reader thanks, Walken! The problem is caused by Flow control was intended to handle the situation where a transmitting computer is sending data faster than a receiving machine can handle it. The IEEE It is still performing flow control, but unlike A buffer is a physical allocation of memory on a device to allow storage of data until it can be moved elsewhere. When flow control is in use, the data buffer is used to store data while the other data it received is processed.
While data is getting bigger, so are the source and destination devices, as well as network pipes. Modern devices are now more capable of handling all that data and processing it fast enough to where flow control is not only unnecessary, but actually a hindrance to better performance.
The general idea is to let the flow control be managed higher up the stack in the form of congestion control. This can be done by applications, and honestly, should be done by the applications as hardware flow control is not application aware.
The long answer? For example, the latest documentation for ESXi 5. I have not seen the best practice recommendation for vSphere 6, yet. The best bet is to contact your specific vendor for their recommendation. Keep in mind that these recommendations can change based on new information, issues seen, etc.
If you do choose to disable flow control, it makes the most sense to disable it on both endpoints. Mismatched configuration could potentially cause performance issues or other problems.
Do you have time for a two-minute survey? Maybe Later. Understanding Flow Control Flow control supports lossless transmission by regulating traffic flows to avoid dropping frames during periods of congestion. IEEE For example, if the connected peer interfaces are called Node A and Node B: When the receive buffers on interface Node A reach a certain level of fullness, the interface generates and sends an Ethernet PAUSE message to the connected peer interface Node B to tell the peer to stop sending frames.
Symmetric Flow Control Symmetric flow control configures both the receive and transmit buffers in the same state. See Also flow-control. Configuring Flow Control By default, the router or switch imposes flow control to regulate the amount of traffic sent out on a Fast Ethernet, Tri-Rate Ethernet copper, Gigabit Ethernet, and Gigabit Ethernet interface.
To disable flow control, include the no-flow-control statement: no- flow-control ; To explicitly reinstate flow control, include the flow-control statement: flow-control ; You can include these statements at the following hierarchy levels: [edit interfaces interface-name aggregated-ether-options] [edit interfaces interface-name ether-options] [edit interfaces interface-name fastether-options] [edit interfaces interface-name gigether-options] Note: On the Type 5 FPC, to prioritize control packets in case of ingress oversubscription, you must ensure that the neighboring peers support MAC flow control.
Here is a white paper that covers some of these subjects. This will help identify any ports that have high pause frames. With the switches i have seen some cases where the received pause frames from an iSCSI target is high, and this obviously slows things down. One thing another user suggested that worked for them to help reduce the pause frames was implement traffic shaping on those ports.
So if you find a port that has it's buffer filled with pause frames, you might try traffic shaping as a work around. All of my iscsi traffic is on separate switches that aren't connected to the core. After doing some more digging into the core switch it looks like 3 of the switches hanging off it have flow control inactive while the other 4 switches have it active and have a ton of Received Pause Frames and Transmitted Pause Frames.
That is likely causing the slow down, I would turn flow control off. What is traversing those switches? That should indicate a buffer overflow usually due to bursts of traffic or heavy volume.
Thanks everyone I will be turning off the flow control this weekend and see how things go. One more question, should I have flow control enabled or disabled on the port that the firewall connects to?
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