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After 10 days (Block Generation) + configured Job immutability period you will see large amounts of putObjectRetention() calls ( 1 for every stored object in the bucket ) Veeam re-assigns all blocks to the next block generation.
For more information about this , see : https://www.veeam.com/kb4470
Veeam does this per VM, so if you have a backup job with 100 VM's in it, and you allow maxActiveSnapshots of 10, you will see 10 parallel VM backups, each of which does the behavior as seen in the chart below.
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