The VMware Knowledge Base provides support solutions, error messages and troubleshooting guides
Backing up a Changed Block Tracking enabled virtual machine in ESXi 6.0.x returns incorrect changed sectors (2136854)
When running virtual machine backups which utilize Changed Block Tracking (CBT) in ESXi 6.0, you experience these symptoms:
- The CBT API call QueryDiskChangedAreas()can sometimes return incorrect changed sectors, which results in inconsistent incremental virtual machine backups.
- Inconsistent virtual machine backups.
When running incremental virtual machine backups, backup applications typically rely on the vSphere API call QueryDiskChangedAreas() to determine the changed sectors.
This issue occurs due to a problem with CBT in the disklib area, which results in the change tracking information of I/Os that occur during snapshot consolidation to be lost. The main backup payload data is never lost and it is always written to the backend device. However, the corresponding change tracking information entries which occur during the consolidation task are missed. Subsequent QueryDiskChangedAreas() calls do not include these missed blocks and, therefore a backup based on this CBT data is inconsistent.
All incremental backups which utilize CBT are potentially affected.
Required steps to ensure incremental virtual machine backup integrity
After the host upgrade is complete, you must create a full virtual machine backup to ensure incremental virtual machine backup integrity. All subsequent incremental backups must reference only the change IDs generated since the full backup (post patch install). You must ensure that the change IDs generated before the host upgrade are not referenced, as this can lead to incorrect sectors being returned by CBT.
- If you are using Eager Zeroed thick virtual disks, just a full virtual machine backup is sufficient to resume incremental virtual machine backups.
- If you are using other types of virtual disks, a full reset of CBT data is required, see Resetting Changed Block Tracking for VMware vSphere virtual machines (2139574).
For more information about supported virtual disk types, see Types of supported Virtual Disks on ESXi/ESX hosts (1022242).
If you are unable to upgrade, use one of these options to work around this issue:
- Downgrade the affected ESXi hosts to version 5.5, and downgrade the virtual Hardware Version from 11 to 10, if necessary. For more information, see:
- Shutdown the virtual machine before doing an incremental backup.
- Do a full virtual machine backup rather than an incremental backup.
Note: Your virtual machine backup solution vendor may have additional information about the impact of this issue on your backup solution, and specific steps that can be applied to mitigate the issue. For more information, contact your backup vendor's support.
- La copia de seguridad de una máquina virtual habilitada para Seguimiento de bloqueo cambiado en ESXi 6.0.x devuelve sectores cambiados incorrectos (2144443)
Request a Product Feature
To request a new product feature or to provide feedback on a VMware product, please visit the Request a Product Feature page.