We found that when performing synthetic operations, transforms, etc, the backup storage needs as much free space as the largest backup or backup copy job.
So with a single jobs of 500 VMs and 76TB you might well need 76TB+ of free space on the backup repository.
We started off with aggregating backup jobs into fewer backup copy jobs but have since reverted to a one-to-one relationship between backup jobs and copy jobs.
(Environment is 600+ VMs and 1PB source data.)
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