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VMware CBT Image Level Backups

I'm looking for a way to determine if CBT is being used or not in my image level backups. It appears that it is not as the backups are taking the same amount of time each time. However, everything is setup correctly, so does anyone know any troubleshooting methods or how I can verify if change block tracking is being used ?

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Re: VMware CBT Image Level Backups


What is CBT?

Did you mean VCB?



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Re: VMware CBT Image Level Backups


CBT is change block tracking which is a feature of VMware. Avamar uses CBT for image level backups. I hope that answers your question. 

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Re: VMware CBT Image Level Backups


*              There is a known issue in the default configuration of the VMware Image Dataset for Avamar 5.0.0-407, 5.0.0-409 and 5.0.0-410 that prevents Avamar from using VMware Change Block Tracking to perform incremental backups of VMware virtual disks

*              The utilize_change_block_list option is not set by default in this dataset, forcing full backups each time

There are two settings that affect the use of change block tracking. Please follow the instructions below to verify change block tracking is correctly enabled for each client (Item 1 below) and for the VMware Image Backup Dataset (Item 2).

  1. Verify that the "Enable change block tracking" is set in the policy settings for each affected client:
    1. In the Avamar Administrator GUI, open the Policy panel
    2. Select the "Clients" tab above the tree on the left
    3. Select an affected client in the right-hand pane, then click the Edit button
    4. Select the "VMware" tab
    5. If "Enable change block tracking" is not checked, check it
    6. Click "OK" to save the settings
    7. Repeat steps 3 through 6 for any other affected clients

  1. Adjust the settings of the default VMware Image Dataset to utilize the changed block list:
    1. In the Avamar Administrator GUI, select Tools => Manage Datasets... from the menu bar
    2. Select the VMware Image Dataset in the tree on the left
    3. Click "Edit" to edit the dataset
    4. Select the "Options" tab
    5. In the "Select Plug-In Type" dropdown menu, select "Windows VMware Image"
    6. Verify that "Use change block tracking to increase performance" is checked
    7. Click "OK" to save the settings
    8. Two "utilize_changed_block_list=true" entries should appear in the Options section of the dataset editor - one for the Linux plugin and one for the Windows plugin
    9. Click "OK" to save your changes

This issue was corrected in Avamar Server version 5.0.1-32.

Please Note: After enabling change block tracking, one additional full backup will be run to generate a change block list. Subsequent backups should run as incremental backups.



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Re: VMware CBT Image Level Backups

Thanks Rudy, I had checked that previously, but I found out that it is an issue of having VM snapshots older than when CBT was enabled in VMware. Avamar ignores the CBT if it detects that previous snapshots are available. We resolved it by deleting all snapshots in vmware that were previous to CBT being enabled. Thanks everyone for the help. There is more information available here:

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