Specification question about CBT reset operation by Veeam

[Asahi]

Hi,

I have a question about the CBT reset operation during an active full backup.

For example, if "Reset CBT on each Active Full backup automatically" is enabled in the settings when creating a new backup job
I assume that the CBT reset operation is performed on the target VM at the time of the first active full backup.
https://helpcenter.veeam.com/docs/backu ... ml?ver=110

As an example, let's assume that VM1 was added when JobA was created and the first backup was performed.

When the backup is executed, you can see the message "Resetting CBT per job settings for active fulls" for VM1 on the Statistics screen of Veeam, and on the vSphere Web Client side, you can see the following "Resetting virtual machine" task for the target VM1.

===
VM1 reconfigured on 12n105.sm.domain within 12n. Changed: config.changeTrackingEnabled: true -> false; Added: Removed: config.extraConfig("ctkEnabled"): (key = "ctkEnabled", value = "TRUE"); config.extraConfig("SCSI0:0.ctkEnabled"): (key = "SCSI0:0.ctkEnabled", value = "TRUE");
===

However, if I add a new VM2 to a backup job (JobA) that has already been backed up, the "Resetting CBT per job settings for active fulls" and "Resetting virtual machine" tasks will not flow to the added VM2. What is the reason why CBT is not reset for this one?

Even if it was an incremental backup session, a full backup operation to retrieve all data would be performed for the newly added VM2, but I would like to know why CBT does not need to be reset for the added VM2.

Kind Regards,
Asahi,
Climb Inc.

[Mildur]

Hi Asahi

Have you checked the vSphere log for VM2. Does it show a CBT reset? CBT reset should always happen for active fulls. Even if it‘s a newly added vm in a backup job.

Please open a case with support and share the case number for our reference. I will follow the case from out side (product management).

Thanks,
Fabian

[yu_ooyama]

Hi Fabian,

I ask the question on behalf of the Asahi.

What I would like to confirm is not the behavior of Active Full, but rather the behavior of adding a VM to an existing job.

Basically, I thought that Active Full would be executed for the first backup of a VM, so CBT would be reset.
However, we add VM2 to a backup job (JobA) that has already been backed up and run it as usual.
At this time, a full backup is performed on VM2, but CBT is not reset.

Is this behavior a specification?

Even if it was an incremental backup session, a full backup operation to retrieve all data would be performed for the newly added VM2, but I would like to know why CBT does not need to be reset for the added VM2.

Kind Regards,
Yuuki Ooyama
Climb inc

[Mildur]

Hi Yuuki

Can you see a CBT reset in your vSphere Logs for the VM2 after you have added this VM to the backup job JobA and run the job?

Best,
Fabian

[Asahi]

Hi Mildur,

At least, when I look at VM2 tasks and events from the vSphere Web Client, I can't find any tasks other than snapshot creation and deletion.
And I can't find the message "Resetting CBT per job settings for active fulls" on the Statistics screen in Veeam.

Kind Regards,
Asahi,
Climb Inc.

[Mildur]

Hi Asahi

Thanks. I can see the same behavior in my V11a lab.
vSphere task logs for the new VM also doesn't show me the necessary steps for a CBT reset:

Code: Select all

1. Modified: config.changeTrackingEnabled: true -> false
2. Snapshot created
3. Snapshot deleted
4. Modified: config.changeTrackingEnabled: false -> true

It looks like it is fixed in V12. I could test successfully a CBT reset for new VMs in a V12 job.

Best,
Fabian

[Asahi]

Hi Mildur,

Thank you for reply.

Wow, thanks for sharing the v12 info.

As an additional confirmation, in Veeam v11a, is an active full backup mandatory after an operation to add a VM to a job?
Is there any disadvantage if the CBT of a VM added to a job is not reset?

Kind Regards,
Asahi,
Climb Inc.

[Mildur]

If you have a deployed a new VM in your vSphere environment and never took a backup of them with any backup tool, this VM never had CBT enabled. There won't be any issues with this completely new VMs.

For existing VMs it is not mandatory, but recommended.
CBT reset on Active full was introduced to protect the VM against possible undiscovered CBT data corruptions when CBT was enabled before on the VM.

Best,
Fabian

[Asahi]

Hi Fabian,

Thank you for reply!

Thank you for the information, I understand that running active full is recommended.

Also, can you tell me more about the fixes in v12?

I believe that in v12, active full will be able to be run for each individual VM in a job.
https://community.veeam.com/blogs-and-p ... tures-2942

Am I correct in understanding that apart from this feature, a new VM added to a job will automatically have its CBT reset?

Kind Regards,
Asahi,
Climb Inc.

[Mildur]

I understand that running active full is recommended.

It's recommended todo a CBT reset on each Active Full. But you don't have todo regular Active Full's.
Especially with reFS or XFS filesystems you wouldn't benefit from space less full backups.
For Network attached storage repositories, active full backups are recommended.

I believe that in v12, active full will be able to be run for each individual VM in a job.

Yes, in V12 you will be able to start active full for a single VM in a Job.

Am I correct in understanding that apart from this feature, a new VM added to a job will automatically have its CBT reset?

Yes, this is what I have tested yesterday. You just add a VM to an existing job. When the job does an incremental run, this new VM has a CBT reset as expected for the first backup.

Best,
Fabian