Netbackup Accelerator for VMware backup - Part 1: Introduction

By | June 24, 2017

Symantec NetBackup is an enterprise-level backup platform that protects your physical and virtualized servers.  A feature NetBackup Accelerator has been introduced with NetBackup 7.5 for file backups and with version 7.6  for virtual machines running in VMware.

What is this?

NetBackup Accelerator uses the VMware Changed Block Tracking (CBT) functionality to identify blocks which have been changed since the last backup. Only those will be backed up and NetBackup Synthetic Full takes care about consolidation into a true Full Backup. So simply put: NetBackup Accelerator is designed to provide full backups for the cost of performing an incremental backup.

How does it work?

At first we should know three powerful technologies used by Netbackup Accelerator:

  • CBT (Change Block Tracking) - is a VMware feature that helps perform incremental backups by tracking disk sectors that have changed. The feature can be accessed by third-party applications as part of the vSphere APIs for Data Protection (VADP).
  • Symantec V-Ray - is a Symantec feature that enables NetBackup to see into virtual machine disk files without mounting them.
  • NetBackup Optimized Synthetics - is a Symantec feature that creates full backup images without reading and shipping entire data set from source to backup storage. Everything happens at the backup storage.

So now, the most important features have been introduced. How backups are performed?

  1. First Full backup - CBT is not used - it does not keep any changes yet. Netbackup backups up virtual machine disk (without whitespace). After doing backup, CBT tracks all changes.

During the next backup e.g. daily backup:

  1. Incremental backup - CBT is used. All the changes since the previous backup are returned to Netbackup. Netbackup also detects deleted blocks (via V-Ray) and does not copy those blocks!
  2. Netbackup performs Synthetic Full backup.


  1. At least Netbackup 7.6.x version.
  2. Storage deduplication such Netbackup Appliance, EMC Data Domain. Please follow for more information about supported platforms.
  3. CBT enabled for virtual machines.

How to configure Netbackup policy with Accelerator, please follow the following article:

Netbackup Accelerator for VMware backup – Part 2: Configuration

Author: Mariusz

Architect (~ 15 years experience based on passion...) with strong background as a System Administrator and Engineer. Focused on Data Center Solutions: Virtualization/Cloud Computing and Storage/Backup Systems. Currently living in Poland.