Appliance Mode (Hotadd) Requirements and Troubleshooting

KB ID: 1054
Products: Veeam Backup & Replication
Version: all
Last Modified: 2016-05-26
KB Languages: DE


Appliance mode (hotadd) fails or configuration assistance is needed.
The following is shown in the statistics window while processing a VM:


Hot add is not supported for this disk, failing over to network mode...

The following can be found within the logs:
“output: --wn:Hot add is not supported for this disk, failing over to network mode...\n”



  • If the Veeam Proxy being used to process the source VM is on a VMFS 3 datastore it must be formatted with proper block size to be able to mount the largest virtual disk of the hot added VMs.
o    1MB block size – 256GB maximum file size
o    2MB block size – 512GB maximum file size
o    4MB block size – 1024GB maximum file size
o    8MB block size – 2048GB maximum file size
  • The Proxy being used to back up the VM must be a Virtual Machine on a host that is able to access the datastore where the source VM’s disks are stored.
  • In versions 5.1 and older of vSphere, the maximum supported VMDK size is 1.98 TB.
  • The disks that are to be hotadd must be SCSI. IDE and pvscsi drives are not compatible with hotadd.
  • VMware Tools must be installed and up-to-date on the Veeam server and any Veeam proxies
  • Datastore needs sufficient space for a VM snapshot
Known Issues: 
  • If the VM disk resides on a Vvol the Hot Add Proxy VM's configuration files must also be on the same Vvol.
  • Hotadd may fail if any disk was created with a newer hardware version than the VM being backed up. For example, if a disk was moved from a hardware version 8 VM to a hardware version 7 VM. To resolve, upgrade the hardware version of the VM.
  • A single SCSI controller can have a maximum of 15 disks attached. To run multiple concurrent jobs with more than 15 disks, you need to add more SCSI controllers to your Veeam Proxy server that is responsible for hot adding the disks. (
  • In case of standalone host connection (no vCenter added to the console), you can only hot add disks of VMs which are located on the same host as the proxy server.  This may require additional proxy servers to be configured on each host in the environment.
  • Hotadd may fail if you are trying to back up the VM through the host added as a standalone server into Veeam Backup Infrastructure but actually being managed by vCenter. The following error message can be found in the source agent log:
Reconfigure attempt failed for VM "" with Vmomi::MethodFault::Exception ("vim.fault.HostAccessRestrictedToManagementServer")
  • Hot Add may fail if the VM you are trying to back up and the proxy server are in different clusters.
  • Virtual Appliance backup job fails after you’ve cloned or restored your VBR server. The reason for that is incorrect UUID reference for Veeam Backup VM which can be found in the following registry key of the Veeam server. Please see
  • Hot Add fails if VM disks being backed up don't have unique ddb UUIDs across the Vcenter, for example if such VMs were deployed from a single template to different hosts.  Please refer to this Vmware article for details:

More Information

Please contact Veeam Support for further assistance:

4 / 5 (17 votes cast)

Report a typo on this page:

Please select a spelling error or a typo on this page with your mouse and press CTRL + Enter to report this mistake to us. Thank you!

Orphus system