Warning during backup policy: Cannot find the CBT tag for the disk "x" in the repository. CBT will be disabled

[ajmayala85]

Hello Veeam Forum

Veeam Case #07751481

Recently updated our VBAz appliances to V8 and we are getting this kind of warnings:

Warning received during the VM "x" backup: Cannot find the CBT tag for the disk "x" in the repository. CBT will be disabled.

Never happened before (we come from v3 to v7 and now V8)

Technical support said there is a limitation from Azure:
"Due to Microsoft Azure limitations, you can apply up to 50 tags directly to a subscription. That is why Veeam Backup for Microsoft Azure is able to create a snapshot only if the tag limit is not reached for the subscription to which the processed Azure VM belongs. If the limit is reached, the operation will fail with a serialization error. For more information on subscription limits, see Microsoft Docs."

Warnings occurs randomly, maybe 1 or 2 on a day and then disappears for a few days, that's the strange thing about it. Is there anyone who has this same problem? any ideas?

Best regards

Alan

[MarcusA20]

Dear Alan,

did you get any more information?
I also saw that message recently.

And I do not get the TAG explanation from Veeam.
The subscription and also the resources do not have near 50 TAGs.
Subscription has 8 TAGs.
VM has 10 TAGs.

They do add some veeam specific TAGs to the snapshots. But that are also only 3 additional.
So it would be interesting to understand what they want to do and what limit they may hit. Because the explanation of the 50 for Subscription makes no sense to me.

Best regards,

Marcus

[MarcusA20]

One thing came to my mind.
I changed the disk yesterday, so that was the first backup after.
The server was migrated from on-premises a while ago and the size was 80 GB.
As we already do pay the next SKU size of 128 GB and space was needed, I just changed it to the 128 GB SKU size.

So maybe this is related to "change block tracking" (CBT) and the mechanism not be able to handle the change disk?

https://helpcenter.veeam.com/docs/vbazu ... html?ver=8

[MarcusA20]

Some more information.
Both disks that show that warning were extended yesterday, before the last backup run.

9:00:20 PM Consistent Snapshot: Snapshot backup of vm-prod-xxxxx-gwc finished successfully 02:30
9:15:08 PM Backing up vm-prod-xxxxx-gwc to backup-prod-01: 100% (5.5 GB transferred)... 10:52
9:17:43 PM Warning received during the VM vm-prod-xxxxx-gwc backup: Cannot find the CBT tag for the disk (ID disk-prod-xxxxx-gwc) in the repository. CBT will be disabled
9:20:23 PM Warning received during the VM vm-prod-xxxxx-gwc backup: Cannot find the CBT tag for the disk (ID osdisk-prod-xxxxx-gwc) in the repository. CBT will be disabled
9:26:17 PM The immutability period (08/14/2025 21:04:24) has been set for restore point 5a78ce2f-6547-4cfd-ba17-7a4c1d2f500a belonging to resource vm-prod-xxxxx-gwc

So I am still interested on what that really means.
A backup was taken, but is it consistent now?

[nielsengelen]

Hi Marcus,

If you change a disk (or size), then this is normal and we have to read all data again to ensure everything is correct and no corruption has occured. This way we can guarantee consistency for the virtual machine.

Please monitor the policy a few days to see if the message comes back and if it comes back, please open a support case to understand the root cause of the issue.

[nielsengelen]

Hi Alan,

This behavior you are seeing looks unexpected unless you made changes to the virtual machines. Please continue working with support to understand why this message keeps returning.