Video Screencast Help
Symantec to Separate Into Two Focused, Industry-Leading Technology Companies. Learn more.

VMWare image backup with Block Level Incremental

Created: 15 Oct 2012 • Updated: 12 Jul 2013 | 4 comments
tarangdce's picture
This issue has been solved. See solution.


I tried configure BLIB with NetBackup, vSphere 5, vmware hardware version 8 (vmx-08) with VMFS 5. Technically BLIB should backup less data in Incremental backup but its reverse in this case. I did configure total of 20 Servers in two different policies one with BLIB enable and other is regular and below are the stats for 5 consecutive incremental backups

BLIB VMWare Incr:- 205 GB

Regular VMWare Incr:- 162 GB

Need your suggestion which to go with for VMX-08 VMs. BLIB or Regular ?

Comments 4 CommentsJump to latest comment

Stuart Green's picture

From a previous post....

Have you already tried disabling and enabling CBT?
If not, consider to try as below.
1) Shutdown VM
2) remove all snapshot of VM
3) remove CBT setting
4) remove *-ctk.vmdk files on datastore
5) enable CBT for both VM and vmdk
6) power on VM
7) take full backup
8) take diff backup
eventually the forum poster reported a fix made available in
But worth the deleting of CTK files to in case CBT failed to identify Changed data Blocks

Tip: Get overview/document your NBU environment. Run 'nbsu' and review the output.

• If this provides help, please vote or mark appropriate solution.

tarangdce's picture

Thaks Stuart.

Its not taking all diffs as FULL backup but comparative little extra size than regular incrementals.
I have a project to setup backup for 900 VMs. I check with vmware team and they check that ctk are created after the 1st snapshot.

There are no snapshot resides for VMs and shutdown 20VMs will need a change and all ...

Yasuhisa Ishikawa's picture

Technically BLIB should backup less data in Incremental backup - why do you think so?
I think it depends on how applications place data and hwo they change data on disk. BLIB backup takes data on block basis, so BLIB takes unchanged data in same block where changed file resides. Incremental backup takes only changed files.
I think it is possible that BLIB backup become lager than incrementals.

BTW, what Stuart point out is very important. If you have never do this, do it first.

Authorized Symantec Consultant(ASC) Data Protection in Tokyo, Japan

tarangdce's picture

Thanks Yasuhisa.

Looks like VMFS 5 has 1mb block size and that may be the reason of larger incremental backups. But here I got an advantage that with BLIB i can restore entire VMs from Incremental as well.

I will see if I can get things done suggested by Stuart.