What happens if HotAdd transport mode requirements are not met during a backup job?

If the transport mode is set to Auto, the backup job will automatically fall back to NBD mode for any disks that cannot reserve a SCSI device node. However, if HotAdd is explicitly forced as the transport mode, the backup job will fail when requirements are not met.

When should NAS transport mode be used instead of SAN mode?

NAS transport mode should be used when virtual machine datastores are on NFS storage rather than Fibre Channel or iSCSI. The access node must be a Windows or Linux physical computer, or a Linux virtual machine, and must have access to the NFS exports and ports through any firewall configuration.

Configuring VMware VSA Transport Modes in Commvault

Name: Configuring VMware VSA Transport Modes in Commvault
Uploaded: 2026-03-12T15:38:36-04:00
Duration: 4 min 57 s
Description: TL;DR Transport mode is configured at the VM group level in Commvault Command Center and determines how virtual machine data is read from VMware storage during backup and restore operations. Auto transport mode is the default setting and uses intellige...

Commvault

03/12/2026

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TL;DR

Transport mode is configured at the VM group level in Commvault Command Center and determines how virtual machine data is read from VMware storage during backup and restore operations.
Auto transport mode is the default setting and uses intelligent logic to select the optimal transport method based on VM location, storage infrastructure, and access node configuration.
SAN mode offers the best backup performance by reading directly from storage, while NBD provides the fastest method for restoring thin-provisioned disks despite slower backup speeds.
HotAdd transport can achieve near-SAN performance but requires virtualized access nodes, shared datastore access, and careful SCSI controller configuration with sufficient device nodes.

This technical tutorial provides a comprehensive walkthrough of VMware VSA transport mode configuration in Commvault, explaining how transport modes determine the method by which virtual machine data is read from VMware storage during backup and restore operations. The video begins by showing where transport mode settings are located within the Commvault Command Center, specifically at the VM group level under the Configuration tab. By default, Commvault uses automatic transport mode selection, which applies intelligent logic to determine the optimal transport method based on virtual machine type and location, storage infrastructure characteristics, and the configuration of virtual server access nodes. The tutorial then examines each available transport mode in detail, starting with NBD and NBD SSL, which are network-based options that offer broader compatibility but slower performance, though NBD excels at restoring thin-provisioned disks. SAN mode delivers the highest performance by reading data directly from storage without traversing the ESX host or network, requiring the access node to have direct LUN access to datastore storage. NAS transport operates similarly for NFS environments, with specific requirements around access node platform and NFS export accessibility. HotAdd transport mode receives particular attention, as it can achieve near-SAN performance by mounting virtual disks directly to the access node, but requires careful attention to SCSI controller configuration, including controller type selection and device node availability. The video emphasizes that automatic mode remains the recommended default because it provides intelligent fallback capabilities when specific transport requirements cannot be met, preventing job failures that would occur if a specific mode were forced without proper infrastructure support.

Chapters

0:00 - Transport Mode Configuration Location
0:54 - NBD and NBD SSL Modes
1:24 - SAN Transport Mode
2:01 - NAS Transport Mode
2:41 - HotAdd Transport Mode
4:14 - Auto Mode Fallback Behavior

Key Quotes

1:45 "SAN mode offers the best performance of all transport modes."
2:53 "HOTAD mode can achieve close to SAN mode performance."
4:42 "The ability to automatically fall back to NBD mode in situations where there are not enough SCSI device nodes or another requirement has not been met is the reason why automatic transport mode selection is the default option."

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