NetBackup Accelerator for Vmware. A whole new World !

NetBackup 7.6Beta is currently being tested by a wealth number of customers. So far the feedback has been very positive especially with regards to one of its new features: NetBackup Accelerator for VMware.

NetBackup Accelerator reduces the backup time for VMware backups. NetBackup uses VMware Changed Block Tracking (CBT) to identify changes made within a virtual machine. Only the changed data blocks are sent to the NetBackup media server, to significantly reduce the I/O and backup time. The media server combines the new data with previous backup data and produces a traditional full NetBackup image that includes the complete virtual machine files

Accelerator has the following benefits:

  • Performs full backups faster than traditional backup.
  • Creates a compact backup stream that uses less network bandwidth between the backup host and the server.
  • Accelerator sends only changed data blocks for the backup. NetBackup then creates a full traditional NetBackup image that includes the changed block data.
  • Accelerator backups support Granular Recovery Technology (GRT) for restoring Exchange and SharePoint applications (using a full schedule only).
  • Accelerator backups support instant recovery of virtual machines. if the Enable file recovery from VM backup option on the policy VMware tab is enabled, you can restore individual files from the backup (full or incremental).
  • Reduces the I/O on the backup host.
  • Reduces the CPU load on the backup host.

With the first release of NetBackup 7.6, GRT restores of SharePoint and Exchange will be supported (Fig1), allowing administrators to restore Site Collection, Library, documents, Webapps or single emails.


Accelerator VMware backups will support MS SharePoint, MS SQL and Exchange Full schedule only, no Incremental or Differential.

Requirements will be NetBackup 7.6 for Master, Media and Client, Proxy Hosts (SLES or AMD64), VMware ESX version 4.0.3 or greater.

Similarly to file system Accelerator backup, supported since NBU 7.5, the Accelerator backup for VMware will generate a Full image on the storage server using blocks from previous image (Synthetic backups). Only the blocks that have changed are transferred from client to media server.

The Accelerator for VMware does not require any changes to the installation process and the feature is available with the standard NBU installation. As with previous accelerator, it requires NetBackup Data Protection Optimization Option license.

One of the key benefits of the new (in NetBackup 7.5) VIP Policy is the possibility to select the VM to backup, by means of a query. This reduces the risk to miss the backup of a VM if the VMware Administrator does not notify the Backup administrator of the creation of the VM to protect. Fig 2 and Fig3 show the Query builder tab and some of the selectable options.



Performing a VMware backup using the Accelerator, leaves the user shocked by the speed reached by backup. The screenshot below shows the throughput of the fist backup without accelerator. Fig4, JOD ID 23 and JOB ID 24


JOB ID 25, 26 and 27 show the speed of the first backup with Accelerator. This is similar to the previous backup since the first accelerated backup gathers all the information needed to facilitate the subsequent bacukps. FIG5


The deduplication rate of the first backup was already as high as 54%. The seconf full backup deduplicated at 98% reducing drastically the amount of data moved via the LAN.

Accelerator Optimization field this time is populated with 0% since this was the first accelerated backup.

Last, Fig 6, shows the real benefits of the Accelerator. Enlapsed time goes from around 10 minutes down to 4 minutes.


I expect that Accelerator performances and benefits will be much higher in a production environment with powerful machines.


Hello Proc1400,

have check against netapp?

how has the better performance?

Accelerator just supports WIN FS and VM?

Hi n.ludwing,

not had the time to run extensive tests yet. I will be waiting for GA.


Hi Ricky,

as ludwing pointed out, NetBackup Accelerator is available for ALL supported client platforms with the exception of OpenVMS.

I member that NB7.5 Accelerator only support WIN FS\LINUX FS?

From 7.6,it can support oracle or other app\db?

Hi Ricky,

Initial accelerator support will only be for SQL and SharePoint and only inside a VM.



I just learnt from PM that accelerator in NBU 7.6 will also support Exchange backups. This is a new feature obtained thanks to a massive work done by Engineering.


Thanks for your excellent post!

You wrote:

"Requirements will be NetBackup 7.6 for Master, Media and Client, Proxy Hosts (SLES or AMD64), VMware ESX version 4.0.3 or greater."

What is Proxy Hosts ? Is it an appliances because you mention SLES (SuSe Linux Enterprise Server) ?

Do we need to install netbackup lcient on each VM to benefit of the accelerator ?

Where is accelerator database located ?

I am asking because in the current release (, once accelerator is enable in the policy, it will create his tracking log/database on the client. For example, on windows client it will be as follow:

C:\Program Files\Veritas\NetBackup\track\<master-server-name>\<media-server-name>\<client-name>\<policy-name>

 (example C:\Program Files\Veritas\NetBackup\track\nbumas01.nammo.local\nbuacorp23\srvtmsco1.mgt.lanprd.nbb\nbb2_bronze_nammo_vmware_lnx_os_dev)

i am really concern about this because we saw some accelerator database (.dat file) growing fast especially for fileserver that have more than 1TB of data.


Thank you for valuable information!

“Accelerator backup for VMware will generate a Full image on the storage server using blocks from previous image (Synthetic backups). Only the blocks that have changed are transferred from client to media server.” , what is “storage server” ?



Hi mikent,

a proxy host is the machine used by NBU to read the snapshot created on the ESX.

It can be a NBU client or a media server, hence it can also be a NBU Appliance.

Please read this post for further info on VMware backup with NBU.

You do not need to install a NBU client inside the VM to use the accelerator but you do need to install the client if you want to run a restore to that VM. In other words, tar binary responsible for the restore only runs if the NBU client is installed.

Normally people decide to install the NBU client inside a single machine, being phisical or VM and use that machine as a target fof the single-file restores.

The path of the Accelerator TL has not changes as far as I am aware.

This 3d can help you understand more about the size of the TL and why it may grow so much

Hi Alex,

From NBU 7.6 Vmware Admin Guide:

The NetBackup Accelerator creates the backup stream and backup image for each virtual machine as follows:
■ If the virtual machine has no previous backup, NetBackup performs a full backup
and uses VMware Changed Block Tracking to track the data in use for each VMDK.
■ At the next backup, NetBackup identifies data that has changed since the
previous backup. Only changed blocks and the header information are included
in the backup, to create a full virtual disk backup.
■ The backup host sends to the media server a tar backup stream that consists
of the following: The virtual machine's changed blocks, and the previous backup
ID and data extents (block offset and size) of the unchanged blocks.
■ The media server reads the virtual machine's changed blocks, the backup ID,
and information about the data extents of the unchanged blocks. From the
backup ID and data extents, the media server locates the rest of the virtual
machine's data in existing backups.
■ The media server directs the storage server to create a new full image that
consists of the following: The newly changed blocks, and the existing unchanged
blocks that reside on the storage server. The storage server may not write the
existing blocks but rather link them to the image.

A Storage Server is a logical server responsible of managing the dataflow of the Storage Type you created.

Please read this 3d for further details.



For SQL and exchange systems this is ok as they are always full. And for all of you that do not use tapes accelerator is ok.

BUT if you are duplicating your incremental backups to tape, then VMware accelerator backup is NOT for you.


Thank you very much now it`s clear. As i see there is no much difference with sintetic backups isn`t it?


Thank you for your quick response.

Based on this technote knowledge based of Vmware, CBT are store in ctk file under each VM folder. Those ctk file are associate to each vmdk and snapshot file. Netbackup 7.6 accelerator for VMware will read those ctk file (same as NT journal for NTFS) in order to get the latest block/disk sector changes during VM machine backup job.

Actually each one of my netbackup client (, for which accelerator is used and enabled through policy, have their own accelerator track log file stored locally under <INSTALL-PATH>\Netbackup\track\<master>\<media>\<client>\<policy>\<DRIVE>\*.dat (see an example in my previous command).

You can even relocate this one in another place if you don't have enough space

What i want to know exactly is the following:

If Netbackup 7.6 use CBT (ctk file) for accelerator for Vmware, does it mean that in that case no accelerator track log are store in the VM machine? therefore there is no need to install netbackup client into the VM machine (unless we have some critical application like SQL, exchange, sharepoint ... running on this VM)?



As you said, Accelerator for Vmware will use CBT to keep track of the changed block hence it wil not create a TL inside any VM OS. In fact, we can also backup powered off machines.

From 7.6 VMware Admin Guide:

Accelerator for virtual machines uses Changed Block Tracking (CBT) technology
from VMware to identify changed blocks. NetBackup requires the changed blocks
when it creates a full virtual machine (synthesized) image. NetBackup is therefore
dependent on VMware CBT for correctly identifying changed blocks. To protect
against any potential omissions by underlying VMware CBT, the Accelerator forced
rescan option conducts the backup without using CBT.

This option provides a safety net by establishing a new baseline for the next
Accelerator backup.
When Accelerator forced rescan is used, all the data on the virtual machine is
backed up. This backup is similar to the first VMware Accelerator backup for a
policy. For the forced rescan job, the optimization percentage for Accelerator is 0.
The duration of the backup is similar to a non-Accelerator full backup.
As an example: You can set up a weekly full-backup schedule with the Use
Accelerator option. You can supplement that policy with a second schedule that
enables the Accelerator forced rescan option, to run every six months.
Note: Accelerator forced rescan is unavailable if the Use Accelerator option on
the Attributes tab is not selected.




Than you for your confirmation about this.

I'll be waiting for 7.6 and test it.

Where are the Track Journal (Track Log) located when you are using Accelerator for VMware - on the client or on the mediaserver (and what's the path)?

I am very interested in the above question - "Where are the Track Journal (Track Log) located when you are using Accelerator for VMware - on the client or on the mediaserver (and what's the path)?"

For VMware accelerator backups there are two (or three) components

The first is the change block tracking on the ESXi host with the vmdk's - this is enabled in vmware and lives with the guest.

The second resides on the master server specifically, in /usr/openv/netbackup/db/snapshot/vm/<client_name>

The third (which looks like a copy of the above) live in the /usr/openv/netbackup/online_util/fi_cntl


As far as I know, there is not TL with Vmware.

Accelerator for virtual machines uses VMware Changed Block Tracking (CBT)
to identify changes that were made within a virtual machine.

Thank you for your answer. I just wanted to make sure that NetBackup didn't use a lot af space on Track Journals somewhere (as it does when accelerator is used in a non VMware policy).

It's my understanding from talking to Symantec Support, that the 'tracking' file used for VMware Accelerator backups is kept on the media server which is acting as the VM backup host. Is this not the case?


Yes and no. There is a tracking file kept on NetBackup's side (I do not have the details of precisely where to hand at the moment) which keeps track of basic meta data about the VM primarily about the VMware cbt file. Additionally VMware tracks changes in the change block file created when the feature is turned on, which is used by VMware/NetBackup to determine what blocks to back up. This is stored in the same place as the VMDK file.

The space kept by NetBackup per client is relatively small (1-2kb per VM) and the size does not relate to the size of the VM.

I'm running into issues using Accelerator for VMware with Data Domain, eventhough the backup is extremly quick, netbackup is duplicating the entire FULL image every time, which create a huge SLP backlog.  Using Data Domain 990 on both primary and remote data centers, does anyone have any experience with that? EMC is recommending going with DDOS since its able to handle synthetic backups differently and not replicate the entire image. But is accelerator trully being seen as a Synthetic when it goes on disk?