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Barracuda Backup
Barracuda Backup

Understanding Changed Block Tracking on Virtual Machines

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The articles in this section refer to Barracuda Backup Legacy Release firmware or newer, and VMware® 4.1 and above with the VMware license which includes access to vSphere® Data Recovery API.

VMware has reported an issue with ESXi version 6.0.x where incorrect changed sectors are returned. When a virtual machine (VM) is running ESXi 6.0.x and Changed Block Tracking (CBT) is enabled, some change areas in data are not reported. When this occurs, that data is not recognized as changed and is not backed up; current and past incremental backups are potentially compromised. For more information, see the VMware knowledgebase solution Backing up a Changed Block Tracking enabled virtual machine in ESXi 6.0.x returns incorrect changed sectors (2136854)[1].

This issue is resolved in VMware ESXi 6.0 patch ESXi600-201511001. For more information, see VMware ESXi 6.0, Patch Release ESXi600-201511001 (2137545)[2].

Use Changed Block Tracking (CBT) to perform incremental backups on virtual machines running on VMware ESX/ESXi. CBT identifies and tracks block changes since the last backup, and stores these changes in log form, greatly reducing the number of backup windows and improving backup window times. Additionally, subsequent replication efficiency and speed are improved.

Barracuda Backup automatically leverages CBT when CBT is enabled for the virtual machine being backed up.

Setting Up Changed Block Tracking

For details on setting up and enabling CBT on virtual machines, refer to the VMware Knowledge Base articles available from the VMware website[3]:

Contact Barracuda Networks Technical Support for information on enabling CBT from the VMware API.

You can enable CBT directly on a VM data source. For a list of requirements and detailed steps, refer to How to Enable Changed Block Tracking through the Barracuda Backup Web Interface.

 

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