Comprehensive data protection for all workloads
Post Reply
indyjake
Novice
Posts: 6
Liked: never
Joined: Oct 30, 2009 1:56 pm
Full Name: Jake
Contact:

Backup method when not using CBT

Post by indyjake » Mar 05, 2013 1:07 pm

If I'm doing an incremental backup and decide to NOT use CBT, what method does Veeam use for determining what to backup within a VM? The reason I ask is that I have a particular VM that has an application installed which touches multiple files every day and modifies the last access time stamp on them. I believe this causes very large incremental backups when using CBT. The vendor of this particular application does not recommend disabling the last access time stamp in the Windows registry (Windows 2003 Server). Thanks for your input.

Jake

foggy
Veeam Software
Posts: 18257
Liked: 1560 times
Joined: Jul 11, 2011 10:22 am
Full Name: Alexander Fogelson
Contact:

Re: Backup method when not using CBT

Post by foggy » Mar 05, 2013 1:35 pm

Jake, Veeam B&R is a block-level solution, so in any case, whether VMware CBT is enabled or not, only changed blocks are copied. When VMware CBT cannot be used, we are using our proprietary changed block tracking engine, that basically scans source VM image, calculates hashes for all blocks, and then verifies what blocks have been changed on your VM compared to the VM image stored in the backup file. This process requires processing of the entire VM (which is longer compared to VMware CBT), but only changed blocks are transferred to the target repository.

In your case, only blocks storing last access time attributes will be changed and, hence, copied during job run (not the whole unchanged files). Disabling VMware CBT will not result in any traffic gain, but, instead, will cause longer backups.

cstemaly
Enthusiast
Posts: 50
Liked: 6 times
Joined: Aug 17, 2012 12:31 pm
Contact:

[MERGED] Question about CBT

Post by cstemaly » Mar 07, 2013 12:07 am

I am running the latest Veeam Backup and Recovery Standard with VMware VMs. I'm backing up some VMs on a daily basis, and all VMs on a weekly basis. These two group overlap somewhat. For example, I have one application server where the data changes daily, so it's in my daily job, but it's also in my weekly job.

I performed some storage vMotions and had to reset the CBT from within vCenter (set CBT to false in the properties of the VM, then delete the *-cbt.vmdk files and reboot a couple of times). It got me to thinking - is there a mechanism whereby Veeam know which blocks have changed since the last daily backup versus which blocks have changed since the last weekly backup if there's only one *-cbt.vmdk file?

Vitaliy S.
Product Manager
Posts: 22984
Liked: 1556 times
Joined: Mar 30, 2009 9:13 am
Full Name: Vitaliy Safarov
Contact:

Re: Backup method when not using CBT

Post by Vitaliy S. » Mar 07, 2013 5:57 am

If you reset VMware CBT Veeam will use its own proprietary change tracking engine to detect changed blocks, see foggy's description above for more details. Thanks!

Post Reply

Who is online

Users browsing this forum: No registered users and 65 guests