Intermittent connectivity loss between Quantum NAS and Commvault VM due to mismatched MTU

Products

• VMware vSphere ESXi

Issue/Introduction

A Virtual Machine (VM) running the Commvault Media Agent is configured to perform backups to a network drive hosted on a Quantum DXi9000 NAS. The backup administrator experiences the following issues:

• The network folder on the Quantum NAS can only be listed/accessed once. All subsequent attempts to access the folder or initiate data transfers fail.

• Basic network connectivity tests (e.g., ping from the VM to the NAS) are successful.

• Network switch logs show no physical connection issues, routing errors, or packet drops on the port level.

Environment

VMware vSphere ESXi

Cause

The intermittent connectivity drops are caused by a Maximum Transmission Unit (MTU) mismatch across the data path.

Upon network configuration review, it was identified that Jumbo Frames were partially configured:

• ESXi Host / Virtual Switch MTU: 9000

• Quantum NAS MTU: 1500 (Default)

Because basic ICMP ping packets are small, they pass through the network successfully, giving the illusion of stable connectivity. However, when the Commvault Media Agent initiates larger data transfers or directory listings, the ESXi host sends packets with payloads up to 9000 bytes. The Quantum NAS, configured with an MTU of 1500, either drops these oversized packets or fails to process the fragmented data correctly, leading to a stalled connection and inaccessible network shares.

Resolution

To resolve this issue, ensure that the MTU size is identical end-to-end across the entire data path.

Engage your internal storage administrator or reach out to Quantum Support to modify the MTU at the NAS network adapter interface.

It is also highly recommended to ensure the Quantum NAS is running the latest stable firmware.

Additional Information

DXi9000 Series Configuration