AAP fails with Linux guest, even if excluded from AAP

[Moebius]

I am using v13 (Windows-based) for the first time.
On Proxmox v9 a backup job backs up some Windows vms and a Linux (Ubuntu) vm. AAP is enabled but the Linux vm is excluded in the AAP options.
The Linux vm *always* fails to back up with the message:
"Failed to perform backup: Failed to prepare disks for backup"
unless it is powered off, or if AAP is disabled for the whole job. The Windows vms back up nicely.

I cloned this vm to an identical one, and the backup jobs fail the same way.
Another identical Linux vm, with the same settings (hardware, options, etc.), backs up with no issues in Veeam v12 (of course without AAP, since it is not available for Proxmox in that version).

Is there a known issue about this that I'm not aware of?

[Mildur]

Hi Lucio

Our support team is fully aware of all known issues.

And since this looks as a technical issue, please provide a support case ID for this issue, as requested when you click New Topic. Without case number, the topic will eventually be deleted by moderators.

Best regards,
Fabian

PS: support can only help if you upload logs https://www.veeam.com/kb1832

[Moebius]

Hi Fabian,

nevermind. I got a good answer from AI for my case. Here it is, maybe this could be useful for other users.

"This is due to the behavior of the native "quiesce" flag combined with how the Proxmox plug-in handles exclusions in Veeam 13.

The technical cause of the behavior:
When the "Enable application-aware processing" checkbox is active globally at the root of the Veeam Job, the plug-in instructs the Worker to send a snapshot request to Proxmox with the quiesce parameter enabled (quiesce=1) for all VMs included in the job.

Excluding the Linux VM within the Veeam sub-menu (Guest Processing -> Applications -> Exclude) exclusively disables Veeam's internal application functions (such as file indexing or database detection), but it does not revoke the quiesce=1 command sent to the Proxmox APIs.

Consequently:

- If the VM is powered on and excluded: Proxmox still receives the order to perform a "quiesced" snapshot. It then attempts to contact the qemu-guest-agent within the Linux kernel to freeze the file systems (fsfreeze). If the agent does not respond (because it is not installed, not running, or the option is not enabled in Proxmox), Proxmox fails to generate the snapshot upstream. Veeam receives the API failure and returns the error: Failed to prepare disks for backup.

- If the VM is powered off: Proxmox detects the stopped state and automatically bypasses any quiesce/agent request, performing a direct crash-consistent backup of the volumes, which therefore succeeds.

- If AAP is globally disabled: Veeam sends a standard snapshot request to Proxmox (quiesce=0), which does not require agent intervention and does not fail."

So in my case, not having the possibility to install the qemu-guest-agent in that vm, I moved it to a separate backup job, with AAP globally disabled on that job.