CBT Corruption Bug Report

[peter.holdridge]

Hello,

Case # 03273439
My first forum post is a bug report with Veeam Backup & Replication. Forgive me if I don't have enough information at first.

Incremental backups of VMware VM's are corrupted if you resize the VM's disks and do not manually reset the Change Block Tracking in VMware.

According to https://www.veeam.com/kb2024, There was a built-in workaround in Version 8 update 2b which allowed you to disable the automatic CBT reset Veeam does.
According to https://www.veeam.com/kb1940, there was a built in solution to fix the VMware bug in Veeam B&R version 8 or later.

Veeam Backup & Replication resets CBT for any resized VMware disk to prevent corruption.

This is not the case however. I have tested this so-called built-in solution and it corrupted the files on my VM. Below are the details of my environment and the test performed.

Environment Details:
[*] VMware ESXi version: 6.0.0 Update 3 (Build 8934903)
[*] Veeam B&R version: 9.5.0.1922 (Update 3a)
[*] VM Name: TestCBT
[*] VM Hardware version: 11
[*] VM VMware Tools version: 10282 (current)
[*] VM OS: Windows 10 1709
[*] Original VM Hard Disk Size: 120 GB (thin provisioned)
[*] Expanded VM Hard Disk Size: 130 GB (Thin)
[*] Tested File: ISO (size 1,112,571,904 bytes) with 1 Install file in it

Test Performed:
[*] Create a new VM with Windows 10. Just install, don’t join to domain, don’t patch.
[*] Run a full backup with Veeam
[*] Extend disk by 10 GB.
[*] Copy in 1 ISO.
[*] Run an incremental Veeam backup.
[*] Restore the VM from the incremental backup to an alternative location.
[*] File compare bit by bit the ISOs vs original by using Windows FC.exe /B File1 File2
https://docs.microsoft.com/en-us/window ... ommands/fc

Test Result:
The FC.exe revealed huge differences in the comparison of the restored ISO to the original. In addition, after mounting and opening the Install file within, Windows reports that the install file is corrupted. Opening the original ISO and running the install on the same VM works without any corruption messages.

Feel free to ask any questions or seek more information that I didn't provide.

[foggy]

Hi Peter, thanks for sharing, we will check your findings and get back with the update.

[foggy]

Peter, we were not able to reproduce the corruption issue internally. Starting version 9.5 U3, Veeam B&R doesn't perform CBT reset for ESX 6.0 and later by default, since it is not required - these versions are not affected by the CBT issue in question natively. If you still can confirm the behavior (file corruption after VM disk resize), we would appreciate you re-opening a case for deeper investigation (logs analysis will be required). Thanks!