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Changing backup compression "on the fly"

Post by glemmestad »


Wanted to ask this "in plenum" in case others have the same question:

What are the implications of changing the backup level "on the fly" in Veeam Backup 4?
My scenario is as follows: All backup jobs recreated after upgrading to Veeam 4, and this time I used the Best compression level for all VMs. All the jobs have been successful and have run a couple of times (full + few differential). Now, I see the CPU load is quite heavy on the servers and want to change the compression level to Optimal instead. I understand it's only subsequent runs of these jobs that are affected (the next differentials), and not the full backup. However, the .vbk would then consist of 90% "Best-compressed-blocks" and 10% "Optimal-compressed-blocks". Over time, this ratio would probably change so that the number of "Optimal-compressed-blocks" increases as more and more blocks change and need to be replaced in the main .vbk file.

My questions is: Is this safe? Is it safe to run in a configuration where the first (full) backup is run as Best compression, and subsequent differentials as "Optimal"? Does it pose a problem when trying to import a .vbk, in case of a .vbk being restored from tape after a few moths?

Like.. how does Veeam know that a certain block is compressed with Best or Optimal compression? Or does it even need to know?

Thanks, Anton :)

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Re: Changing backup compression "on the fly"

Post by Gostev »

Hi Even, your description above on what happens when you change compression level for the existing backup is correct. Compression level for each block is specified in the block's metadata, so importing VBK with blocks having different compression will work fine. Thanks :)

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