Veeam Synthetic Backup Explained

The way Veeam’s Synthetic Backup works is that after the first full backup, all subsequent backups are incremental, meaning just the changes from the last backup run, forever. Veeam Backup “injects” the changes into the full recovery file (.VBK) and then also saves any data replaced during this process into the reversed incremental changes file (.VRB). The .VBK file is always a full recovery file and the largest file in the directory. The .VBK file also has the most current modified date as it gets updated after each backup cycle.

The .VRB files do not change, as they contain the .VBK data blocks which were replaced by incremental data for that particular incremental backup run. To restore or roll-back to a particular date/time, all related .VRB files are applied to the .VBK file in the required order to get you back to that point-in-time.

The retention policy specifies how many of the .VRB files you want to keep, this also then corresponds to how “far” you can roll-back. If the retention policy is set to 14, then the 15th time the backup job runs it will delete the oldest .VRB file.

Veeam utilized the same metholody for it’s Replication except that the changes get “injected” into the .VMDK file on the target, there is no .VBK file. There are .VRB files and this is what allows for replication roll-back.

If you archive the .VBK and associated .VRB files as a set to tape, you can recover them back to disk if needed and import them into Veeam Backup 2.0 to roll-back or recover to any point in time in that set.

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8 Comments

  • dj medieval says:

    Doug,

    You’re following me on twitter. I noticed, so I came to this blog to check out what’s up, and realized your company produces products that compete with Vizioncore’s offerings, in particular the Veeam Monitor. vCharter Pro is a nightmare and I wish it would end. I hope I can make contact with you in the next few days, because I’d really like to evaluate Veeam in our environment, and I’m glad to work with a company that allows its engineers to post cool stuff on blogs and twitter without dropping the hammer on them.

    DJ Medieval

  • Drew Green says:

    Thanks for this explanation. I was a bit confused at how this worked, but this cleared things up for me.

  • Albert says:

    Yes indeed, Veeam is great, this product is must have with VMware vSphere product :-)

  • Mike says:

    Great explanation! Are the incremental and reversed incremental files compressed and/or dedupe?

  • Anton Gostev says:

    Yes, they are compressed and deduped.

  • Hussain says:

    I’m still a bit confused on how to configure the retention policy. Before Veeam backup, I used to use the Backup Exec, Weekly Full, Daily incremental and Monthly Full Backup.

    Now I do have Veeam as well as Backup Exec, What I want to achieve is to have Veeam to run Weekly as Full Backup and starting from Sunday towards Thursday as incremental. Backup Exec will backup the VBK and VIB files on a daily basis.

    For how long shall I configure the retention policy?

  • Hussain says:

    Hello,
    For replication, we can set the Retention Period as 1, which will end up having the VM files and 1 .vbk file. This will save space on the VMFS Datastore Destination.

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