1. Test the performance in the scenario where the storage is connected through iSCSI. If the storage is connected through switches, the bandwidth cannot reach the normal level of the storage, which may be caused by packet loss. Run the ifconfig command in the minisystem of the storage system to check whether packet loss occurs on the service port. If packet loss occurs, run the ifconfig command twice when services are running. The overunns value changes.
To resolve packet loss during network transmission, enable flow control on the switch port.
2. Traffic control
Traffic control is a technology that prevents packet loss due to network congestion. After flow control is configured on both ends of a link, if congestion occurs on the local device, the local device sends a message to instruct the peer device to temporarily reduce the rate at which packets are sent. After receiving the message, the peer device stops sending packets to the local device regardless of the working rate of the interface. This prevents congestion.
On the network shown in Figure 1, SwitchA communicates with SwitchC through SwitchB. The flow control mechanism is as follows: 1. 10GE1/0/1 on SwitchA is connected to 10GE1/0/2 on SwitchB, and the auto-negotiation rate is 10000 Mbit/s. Data packets are transmitted between interfaces at a rate of 10000 Mbit/s.
2. The maximum transmission rate of GE1/0/1 on SwitchB is 1000 Mbit/s. When congestion occurs during packet forwarding, SwitchB buffers received packets. When the number of buffered packets reaches a certain value, the forwarding capability of GE 1/0/1 is exceeded, and packet loss may occur.
3. After flow control is configured on 10GE1/0/1 of SwitchA and 10GE1/0/2 of SwitchB, 10GE1/0/2 sends a Pause frame to 10GE1/0/1 of the peer device, instructing 10GE1/0/1 to stop sending packets temporarily. After receiving the Pause frame, 10GE1/0/1 temporarily stops sending packets to 10GE1/0/2. The pause duration is carried in the Pause frame. When the congestion persists, 10GE1/0/2 keeps sending Pause frames to 10GE1/0/1.
4. GE 1/0/1 continues to send cached data packets until the congestion is cleared.
5. After the congestion is relieved, SwitchB does not send Pause frames to SwitchA, and SwitchA continues to send data packets at a rate of 10000 Mbit/s.
3. Configuration Method
Use a Huawei CE6800 10GE switch as an example. After logging in to the switch through a serial port or remotely, run the following command to configure traffic control on the target port 10GE1/0/1:
<HUAWEI>system-view [-HUAWEI]interface 10GE1/0/1 [*HUAWEI-10GE1/0/1]flow-control [*HUAWEI-10GE1/0/1]commit [*HUAWEI-10GE1/0/1]quit [-HUAWEI]
