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OceanStor 5500 V3 Adding iSCSI Links for a Remote Replication Fails

Publication Date:  2017-12-23 Views:  90 Downloads:  0
Issue Description

Under the condition of front-end Fibre Channel networking, a user configures the remote replication feature on a storage system. However,adding iSCSI links to the remote device fails. The message is "The communication is abnormal or the system is busy."

Handling Process

                    Step 1  Check whether iSCSI can be pinged

In minisystem mode, ping the IP address of the iSCSI port on the remote storage system.

l  If the IP address cannot be pinged, the network configuration is incorrect.

l  If the IP address can be pinged, the network configuration is correct. Go to step 2.



Step 2    
Test whether the OM module can successfully execute commands.

On the CLI, select any command (for example, show storage_pool general) to test whether the OM module can successfully execute commands.
l  If no command output is returned, the problem is not the one described in this case.

l  If the command is normally executed, go to Step 3.


Note: If command output is returned, the command is normally executed.

   Step Step 3     Collect log information generated at the problem occurrence time, and search for [EPL][eplRecvLinkClaspReq. The following key information exists:


 
Step 4    
In debug mode, run epl showarray -a 0 to query information about remote replication links.
On the two controllers, there are eight Fibre Channel remote replication links in total, indicating that the problem described in this case exists.


Note: In the preceding figure, four Fibre Channel remote
replication links are created on each of controllers A and B.



Root Cause

A remote replication supports a maximum of eight links. Fibre Channel and iSCSI share this quota. (Remote replication links are established using a proprietary protocol. Fibre Channel links are automatically established. iSCSI links are established after being added. Links between a host and the storage system do not share the quota.) After the quota is used up, information about subsequent remote replication links cannot be obtained and adding links fails. If more than eight Fibre Channel links are established first, subsequent iSCSI links cannot take effect.

Solution


In the scenario where Fibre Channel switches are used, you are advised to use zones for isolation. When you take workarounds, pay attention to the service impact. If no service is running, you can try the following method: Remove some of the Fibre Channel cables and add iSCSI remote replication links again.

END