Breaking the Link Between the Host and Storage Array Connected by Brocade HBA

Publication Date:  2013-06-09 Views:  336 Downloads:  0
Issue Description
Product and version information:
  •  S5000T V100R001 and V100R002
  •  Fiber Channel HBA: Brocade 425/825
The host and storage array form a DAS network, as shown in Figure 1-1. The connection mode of the Fiber Channel host port is adaptive (Loop then P2P). After the connection is established, the rate of the Fiber Channel port is modified or the host is rebooted. Then, the connection is interrupted, and the ISM displays that the initiator is not connected.
Figure 1-1 DAS networking

The connection mode of the Fiber Channel host port is adaptive (Loop then P2P). After the connection is established, the rate of the Fiber Channel port is modified or the host is rebooted. Then, the connection is interrupted, and the ISM displays that the initiator is not connected, as shown in Figure 1-2.
Figure 1-2 Connection status of the initiator
Alarm Information
None
Handling Process
Step 1 Run the chgportparam command to set a 500 μs latency for the link creation.
For details about how to run this command, run the help –c chgportparam command. The command output is shown in Figure 1-3.
Figure 1-3 Command output of help -c chgportparam

Step 2 Run the chgfcmode command to set the storage array to P2P mode for connection.
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Root Cause
In adaptive mode, the Fiber Channel host port of the storage array is connected to the host. If the Fiber Channel physical link is disconnected, the link initiation to rebuild the link between the Fiber Channel host port and HBA starts following the sequence of "Loop then P2P". The Brocade HBA does not support the loop mode. However, loop primitive negotiation returns a wrong value to provide the loop mode for the storage array. As a result, the connection between the storage array and host HBA cannot be established.

As a comparison, the EMC array also cannot be connected to the Brocade HBA.
Suggestions
  •  To use the Brocade HBA in a DAS network, you must run the chgportparam command to set a 500 μs latency and run the chgfcmode command to set the topological mode to P2P.
  •  After the connection is established, do not modify the rate of the Fiber channel link.

Reference Information
1. Brocade officially claims that the Brocade HBA does not support the loop mode and cannot be directly connected to the storage array.
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NOTE:
It is verified that EMC's storage array also cannot be connected to the Brocade HBA.
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2. Since the storage array does not support topology negotiation, you need to find another way of establishing the connection between the storage array and Brocade HBA. That is, use the CLI command to postpone the storage array sending Flogi for 500 μs. As a result, the HBA sends Flogi first, and the P2P connection can be established.
3. After the storage array supports topology negotiation, the HBA and storage array will implement link negotiation when the Fiber Channel rate is modified or the host is rebooted. Since the adaptive mode of the storage array is "loop then P2P", the loop primitive negotiation is first carried out, when the HBA responds to loop initiation primitives such as LIP, LISM, and ARB (F0) that are sent from the HBA. As a result, the loop mode forms for the storage array. The HBA does not support the loop mode. Therefore, the connection between the storage array and HBA cannot be established, as shown in Figure 1-4.

 

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