Cannot enable Changed Block Tracking (CBT) for this virtual machine because the machine has snapshots
We are getting warning message "Cannot enable Changed Block Tracking (CBT) for this virtual machine because the machine has snapshots" on some VM with existing snapshots. We have vmware vsphere 6.0 Update 2 and vmware vsphere 6.5a. My understand is vsphere 6.0 update 2 includes a fix for CBT but not sure about 6.5a (see known issue in http://pubs.vmware.com/Release_Notes/en/developer/vddk/65/vsphere-vddk-…). I have few questions:
1. While I have CBT enabled and getting the warning. Is that mean Acronis backup will automatically backup the VM without CBT?
2. With both vsphere 6.5a and 6.0 U2, do I have any concern?
3. Do I need to recreate all my full backup?
Regards,
Aldous
Aldous thank you for your posting!
Indeed, there is a known issue for vSphere 6.5 GA. Have you created snapshots manually for these machines? The issue can be caused by these snapshots which cannot be deleted automatically. Normally, snapshots will be deleted after the backup is successfully finished, but this does not apply to manually created snapshots.
Another solution will be to disable CBT. You do not need to recreate the backups after that.
- While I have CBT enabled and getting the warning. Is that mean Acronis backup will automatically backup the VM without CBT?
No, Acronis Backup 12.5 will not attempt backing up without CBT; you will need to change the settings manually.
- With both vsphere 6.5a and 6.0 U2, do I have any concern?
These undeleted snapshots cause the problem and not the vSphere version, so the update or downgrade will unlikely solve the issue. Please either delete the snapshots or disable CBT in the backup options.
I hope I could answer your question. If you have further questions, please let me know.
Hi Elizaveta,
Thanks for the reply. Unfortunately, my questions weren't clear.
We manually created VM snapshots for system admin reasons and usually keep the snapshots for few days to a week. We have CBT enabled on all our backup plans.
When a manual snapshot created and backup ran, we got following Warning message but the backup of the VM completed.
Warning
The virtual machine may be backed up without using Changed Block Tracking (CBT) because the machine has snapshots. For the details, see https://kb.vmware.com/s/article/1020128
To avoid this warning, either disable CBT in the backup options or delete the snapshots.
In the message, it referred to a VMware KB. That's why I was asking the questions about the vmware version that we have. I revised my questions below:
1. While I have CBT enabled and getting the warning. However, the backup was completed. Then, how was the backup completed? Will it be a good backup?
2. The acronis warning message referred to vmware KB, 1020128. According to the KB, there were issues with CBT causing backup issue with CBT enabled while manual snapshots exist but it's referring to certain ESXi version and updates. We have vsphere 6.5a and 6.0 U2; are we affected by the CBT issue in this vmware KB?
Regards,
Aldous
Hello Aldous,
1. Changed Block Tracking (CBT) is a VMware feature that helps to perform incremental backups, but is not essential for that. We use CBT only for accelerating the backup creation, as it tracks the changes in blocks. Taking incremental backups will take longer with CBT option disabled, however the size of them will still be "incremental".
2. The described behavior is not an issue in a particular ESXi versions, it's one of the requirements for the CBT feature to work
- The virtual machine must have zero (0) snapshots when CBT is enabled, for a clean start.