B&R 9.5 : Enable CBT for only some disks of a VM ?

[JuA]

Hi,

For some reason, I would like to backup VMs having 4 disks, enabling CBT only for 3 of the disks.

VMware allows to do this, but then Veeam re-enable CBT for all disks when the backup job starts.

Is-it possible to avoid this ?

Regards,

[Andreas Neufert]

Can you please share why you want to do this?
Without CBT Veeam will operate in Snap and Scan backup mode, reading from non CBT disks 100% at every backup.
CBT do not affect performance of the VM.

[JuA]

Of course yes, I know this


The reason is we reached an undocumented ESXi6.5 limit : Maximum active CBT Disks = 1024.

The limit is in fact not exactly 1024, but it's between 1024 and 1150.

All our VMs have one small boot disk. Disabling CBT for this disk will have a low impact on backups (300VM*128M = 38G)


It would be a workaround to wait for a real solution (additionnal servers).

[Andreas Neufert]

Oh I never ran into this. Tried to google it without luck. Please share if you can a VMware documentation or support case number so that I can follow up with VMware.

There is no way in disabling CBT for specific disks on the Veeam side. You can potentially group some smaller VMs in Jobs and disable CBT in our Job-Storage-Advanced-VMware section and disable CBT for those? Or backup some with our Agents in the meantime (no extra license needed).

[JuA]

It's an uncommon issue for VMware too : we worked 3 month with them to catch this . Case 19098088103.


They said they may add this value in the "Configuration Maximums" document.

I can't say more about VMware's plan about this, what they said at the end is quoted as confidential ("Not to be shared outside the work on this specific case").


Thank you for your additional workaround ideas, but they are too difficult to manage on lots of VMs.

[Andreas Neufert]

Question from our team. How does this affect the Veeam Backup? Will we fail with a specific warning at enabling CBT of specific VMs that are processed? Can you please share any logs?

[JuA]

Veeam is not directly affected (The backups run and exit with a successfull status). The main observation is that after a job is finished, all the the saved VMs which are hosted on an impacted host have the "consolidation needed" status.

[Andreas Neufert]

I am sorry but there is nothing we can do on the Veeam side. I see that the OS disk is not that important, but the idea of Veeam is always to backup the whole VM with all disks to be able to do Instant VM Recovery and other Veeam features. For example the Explorers automatic processing depend on the OS disk and the registry.

As the main issue here is the VMware, we have asked VMware to comment about it and our contacts formed a feature request to make this setting a softcoded one, so that customers can increase it.
It will take some time.

So in the end I suggest to install Veeam ONE (30day trial) to identify the VMs with the least changes and create separate jobs for them with disabled CBT. You can create a list of these VMs and exclude them in the current job processing. Potentially automatically by PowerShell edits.

[JuA]

I don't search for a solution to this issue with Weeam, the situation is clear on our side. I just gave precision you asked for your team in your previous message.

Regards,