Change block tracking

The wording in the Change Block Tracking manual is a little unspecific. It says that upon purchase, we will be given a link to download the current client edition, and previous editions. So is the change block tracking upgrade purchase only applicable to current versions, or do we get the new client versions also?

Is the driver just an add-on to the current client? Or is it built in to the existing open source executables?

How much of a performance increase should we see?

Also, if I buy X number of licenses, but have Y number of clients where Y > X, can I specify which clients should receive the upgraded client in the web interface?

Yes, you will have the next versions also …
I’ve purchased one CBT license for testing. When you purchase, you receive an URL to a special repository containing the CBT client versions.

From this page you have a link at the bottom of the page “Download update URL file for server” which download a file called server_update_location.url.
Placing this file in /var/urbackup enable the client autoupdate of CBT version in replacement of the normal version
After that, you must activate this parameter in the client settings to enable CBT:


Do we have to reboot the client after upgrading the cbt client version, eg update from 2.0.25-cbt to 2.0.26-cbt ?
Where can we check if the CBT is really used ? Because for the moment i didn’t notice a real improvement on the client i’ve activate for CBT …


Yes, license is for the driver with driver version 2.x updates included. It is a separate Windows driver. The UrBackup client itself is unmodified (except the version number) from the installer found on the web site.

The performance difference is variable. E.g. on the example below it is smaller, because the PC has an SSD which can read all the 230GB of used space in about an hour. With CBT it (in this case) only needs to read 15.4GB which still more than halves the backup time and uses less CPU in that time.

So because it only reads (and hashes) 15.4GB it uses a lot less CPU (good for laptops on battery) and is faster. If you have a bigger volume or smaller changes it can have an even larger performance impact.

If it is active and the whole volume hasn’t been written to it will add a log line in the image backup log:

The CBT should take effect after a reboot and the second image backup after the reboot. If this does not show up I would of course be interested in solving this.

On the roadmap for 2.x (with regards to CBT) are:

  • Use CBT information for file backups as well. This significantly improves performance of backups of larger files such as virtual machine images
  • Use CBT information for image restore (special restore cd), such that the restore is as fast as an incremental image backup with CBT (incremental restore) if the volume is restored to the original volume

Does CBT work with the SYSVOL partition?

Unforunately it does not show up.
I’ve installed the 2.0.25-cbt client and rebooted the client. In the meantime, client have been upgraded to 2.0.26-cbt without a reboot.
There have been few full image backups running with the cbt option NOT activated in the client settings (set to “-”) with 2.0.25-cbt and 2.0.26-cbt client version.
Two days ago i set the cbt client settings to ALL, run a full image backup the evening and another full the next morning :

Should i see the driver somewhere in the Device manager ? Check something else ?


You can check if it is active for a volume by running

cd C:\Program Files\UrBackup
urctctl.exe status c:

in a admin cmd.

I would also appreciate if you send me debug logs (enable_debug_logging.bat + restart) and the Windows version involved. Thanks!

Currently it doesn’t do incremental backups for SYSVOL at all and then you could probably get away with just assuming it never changes (needs to be confirmed, though).

I send you logs by mail.
Windows 2012 R2 Server Standard Edition, up to date

Ok now it seems to be ok after enabling debug and rebooting the client :

Tried it out on one machine:

Cannot open volume. Last error: 5

Also, will it show the CBT client version in the web interface? Or only the generic client version?

That would indicate that it cannot open the volume (ACCESS_DENIED). Did you run it as administrator?

I wonder if I need to add a GUI component to show the CBT status.

The version will be shown with a “-cbt” appended.

I downloaded the UrBackupUpdate.exe from the link and then ran it under my account on the machine that is an Administrator. Do I specifically need to “run as Administrator”?

That would be helpful.

This client is not showing the -cbt appended to the client version.

I was assuming you ran urctctl.exe status c:? Where else is the error message shown?

The server only updates the version string on client reconnects (i.e. take client offline for 5min) or a few minutes after the server updates a client. This could be the reason for that.

Ohhhhh, yes. Administrator command prompt. I misunderstood.

I reran the command from the same prompt and it now reports correctly. Maybe it took a few minutes?

Weird. It had the error while opening the volume, though. Could be another program locking the volume. UrBackup itself did that at some point (albeit with the shadow copies).