A data center uses a Cisco MDS 9710 director with multiple line cards. The storage network includes several host servers connected to the director via 16 Gbps FC connections. Recently, the engineering team deployed a new storage array that supports 32 Gbps FC. To take advantage of the higher speed, they upgraded the host HBAs to 32 Gbps. However, after the upgrade, some hosts are experiencing intermittent connection drops. The team notices that when a host disconnects, it takes approximately 30 seconds to reconnect. The link lights on the host and switch ports are green. The switch logs show 'VSAN 100: Port fc1/1 is down (link failure)' messages. No other errors are reported. The MDS line cards support 32 Gbps, and the ports are configured with the 'speed 32000' command. What is the most likely cause of the intermittent drops?
A mismatch (e.g., host at 16 Gbps, switch at 32 Gbps) can cause intermittent link drops.
Why this answer
The most likely cause is a speed mismatch between the host HBA and the switch port. Although the switch port is set to 32 Gbps, the HBA might be set to auto-negotiate or default to 16 Gbps, causing instability. The 30-second reconnect time is typical of speed negotiation failures.
Incompatible SFPs would cause persistent link failure, buffer credits cause throughput drops but not disconnects, and zoning would block connectivity.