Article ID: 54029
Article Type: Troubleshooting
Last Modified:
After a virtual machine disk (VMDK) is expanded beyond 128 GB or any doubling of 128 GB, VMware ESXi 4.x or ESXi 5.x can return incorrect information about virtual machine disk sectors, and Changed Block Tracking (CBT) can produce unrecoverable backups.
This is a flaw in VMware APIs used by backup software, and can lead to data loss if not addressed immediately.
SP9 provides a crucial fix to prevent data loss. As a result of applying this service pack, the time and disk space for backups is increased.
Any virtual machine is at risk if VMDKs have been expanded beyond 128 GB, 256 GB, 512 GB, 1024 GB, or any doubling of 128 GB. For example, the issue can occur after expanding a VMDK from 100 GB to 150 GB, or after expanding a VMDK from 150 GB to 300 GB.
Any backup performed since the disk expansion can contain invalid data, including full backups.
The VMware command QueryChangedDiskAreas("*"), which is used to return a list of allocated disk sectors, returns an incorrect list of allocated virtual machine disk sectors and does not return allocated portions of the VMDK file.
For more information, see QueryChangedDiskAreas command returns incorrect sectors after extending virtual machine vmdk file with Change Block Tracking (CBT) enabled (2090639).
For Service Pack 9 and later, the Commvault software automatically detects expanded disks and resets CBT as described below.
The following HotFixes resolve this issue for all virtual machines:
To access one of these HotFixes, use the links above or go to Cloud Services, log in, access the Download Center, and select ServicePack/Hotfix > SP8.
Install the HotFix on Virtual Server Agent (VSA) proxies.
After applying the HotFix or Service Pack 9, the following actions are taken:
You can use the CheckChangeTracking tool to reset CBT on specific affected virtual machines. This tool resets CBT without requiring that the virtual machine be restarted.
The tool automatically re-enables CBT for the next backup job, which will back up all blocks for VMDKs even if an incremental backup is requested. CBT is also enabled for future incremental backups.
As a result of resetting CBT (by using the current service pack, applying the HotFix, or using the CheckChangeTracking tool), the time required for backups increases because the first backup after resetting CBT backs up all blocks for any virtual machines on which CBT was reset. This change can also increase disk storage requirements for backups. The change does not affect scheduled backup cycles or data aging.