The provided EMS logs from both nodes show a symmetrical failure pattern. Node netapp-EmA (at site A) reports the loss of its HA interconnect and can no longer see the FC-to-SAS bridges at site B. Simultaneously, node netapp-EmB (at site B) reports the loss of its HA interconnect and can no longer see the bridges at site A. This reciprocal loss of connectivity to the remote site's storage infrastructure indicates a failure in the communication path between the two sites. In a Fibre Channel MetroCluster, this path is the Inter-Switch Link (ISL). The failure of the ISL severs the connection between the two SAN fabrics, causing each controller to lose access to its partner's mirrored storage plex, which triggers the "DISK REDUNDANCY FAILED" message.

A. the ATTO bridge on siteB2: A failure of a bridge at site B would not cause node B to lose connectivity to the bridges at site A.

B. the SAN switch siteA2: A failure of a switch at site A would not, by itself, explain why node A also lost its path to site B.

C. the SAN switch siteB2: A failure of a switch at site B would not, by itself, explain why node B also lost its path to site A.

1. NetApp Technical Report 4705

"MetroCluster Solution Architecture and Design": Section 3.2.2

"Fabric-attached MetroCluster storage

" describes the architecture where switches at each site are connected by Inter-Switch Links (ISLs). It states

"The ISLs carry all storage and cluster traffic between the two sites." A failure of these ISLs would sever this connection

leading to the symptoms observed in the logs.

2. NetApp ONTAP 9 Documentation

"MetroCluster management and disaster recovery": The section on "Troubleshooting switch issues" outlines procedures for verifying connectivity. A common step for a site-to-site communication failure is to check the health and status of the ISL ports on the FC switches

confirming that an ISL failure is a primary cause for such events.

3. NetApp ONTAP 9 Documentation

"Messages and EMS reference": The description for the cf.rv.notConnected message indicates "The HA interconnect connection has failed. This might be due to a network problem or a problem with the partner node." The simultaneous occurrence on both nodes points to a network problem between them (the ISL). The bridge.removed message confirms the loss of visibility to the remote storage hardware.