Changed Block Tracking (CBT)

[tthomas1@ebsco.com]

Hello,
I've been using Veeam for several years now to back up a few physical Windows servers and a small number of VMs. For each of these, I enable CBT based on what I read when I first configured Veeam - it appears to improve various processes, with the main downside being that reboots are required during every upgrade. I verified the VMs are running the correct machine version.

I recently heard a Veeam technician say that there's no need to enable CBT unless your content contains large database files. I've not specifically seen that documented anywhere but thought I would throw the question out here. Is CBT commonly used when backing up physical servers? What about VMs? Any "best practices" that someone can recommend? Thanks in advance!

[Mildur]

Hello Tim

The Veeam Technician is correct. For Veeam Agent, there are two CBT methods:
- Default CBT mechanism
for NTFS volumes only, leverages Master File Table to track changed blocks

- Veeam Changed Block Tracking Driver
Works for all filesystem types and is the recommended for large databases

For VMware VMs, there is only one type of CBT. It works out of the box and does not require special drivers:
https://helpcenter.veeam.com/docs/backu ... ml?ver=120

Best,
Fabian

[tthomas1@ebsco.com]

Thank you Fabian! I should have clarified that for the VMs, we don't have vCenter added to Veeam Backup & Replication. We just have the agent installed on the VMs, so they are basically backed up the same way as a physical server. Does the same advice apply?

I had previously noted the phrase that the Veeam CBT driver "keep track of changed data blocks in a more efficient way". I had not really paid attention to the next line about large database files. Only one of the servers in question has a database (as far as I know) and it is a flat file database with over 1 million files, with a TOTAL size of 91GB. From what I can tell the files are in the KB range. I presume this would not be a candidate for CBT then?

[tthomas1@ebsco.com]

One other question: any issue with uninstalling the CBT driver? I would assume it just goes back to the default. It would be great to remove it and not have to reboot anymore.

[Mildur]

Hi Tim

Moved your topic to the agent forum

Does the same advice apply?

Yes, Veeam Agent doesn't care if installed on a virtual or physical machine. Both CBT methods in Veeam Agent works the same way for virtual machines.

Only one of the servers in question has a database (as far as I know) and it is a flat file database with over 1 million files, with a TOTAL size of 91GB. From what I can tell the files are in the KB range. I presume this would not be a candidate for CBT then?

I don't have comparison numbers to share about job duration difference for such a database type. If you want to remove the CBT driver, it would be nice if you can share backup job duration between an incremental backup session with the CBT driver and incremental backup with the default CBT mechanism.

One other question: any issue with uninstalling the CBT driver? I would assume it just goes back to the default. It would be great to remove it and not have to reboot anymore.

No, Uninstalling CBT driver won't cause issues. The next job run may take longer because "CBT was reseted".

Best,
Fabian

[tthomas1@ebsco.com]

Thanks Fabian, makes sense. I'm debating whether it makes sense to remove it. I'm starting to think it does. Thanks for the tips!

[tthomas1@ebsco.com]

One last question: does UNinstalling the CBT driver require a reboot?

[Mildur]

Yes, installation, removal and updating the driver will require a reboot.

Best,
Fabian

[tthomas1@ebsco.com]

Thanks, that's what I would have guessed. Will likely uninstall during our next round of upgrades, whenever that occurs. Thanks again!