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Virtual Appliance

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The Virtual appliance mode is not so efficient as the Direct storage access mode but provides better performance than the Network mode. The Virtual appliance mode is recommended if the role of a backup proxy is assigned to a VM.

In the Virtual appliance mode, Veeam Backup & Replication uses the VMware SCSI HotAdd capability that allows attaching devices to a VM while the VM is running. During backup, replication or restore disks of the processed VM are attached to the backup proxy. VM data is retrieved or written directly from/to the datastore, instead of going through the network.

The Virtual appliance transport mode can be used for all operations where the backup proxy is engaged:

Backup
Replication
VM copy
Quick migration
Full VM restore
VM disk restore
Replica failback

Requirements for the Virtual Appliance mode

To use the Virtual Appliance transport mode, make sure that the following requirements are met:

The role of a backup proxy must be assigned to a VM.
The ESX(i) host on which the backup proxy is deployed must have access to the datastore hosting disks of VMs that you plan to process.
The backup server and backup proxy must have the latest version of VMware Tools installed.

Limitations for the Virtual Appliance mode

If you use VMware vSphere version 5.1 and earlier, the maximum size of a VM virtual disk be processed must not exceed 1.98 TB.
If you plan to process VMs whose disks are located on a VMFS 3 datastore, you must format the datastore with a proper block size to be able to mount large VM virtual disks to the backup proxy or helper VM:

1 MB block size — 256 GB maximum file size
2 MB block size — 512 GB maximum file size
4 MB block size — 1024 GB maximum file size
8 MB block size — 2048 GB maximum file size

This limitation does not apply to VMFS-5 volumes that always have 1 MB file block size.

Backup and restore of IDE disks in the Virtual appliance mode is not supported.
The paravirtual SCSI controller (PVSCSI) is not supported for HotAdd; use the LSI controller instead.
Backup and restore of SATA disks in the Virtual appliance mode is supported if you use VMware vSphere 6.0 and later.